LI-COR LI-7500 Instruction Manual
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LI-COR LI-7500 Instruction Manual

Co2/h2o analyzer
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LI-7500
CO
/H
O Analyzer
2
2
Instruction Manual
®
Environmental Division

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Summary of Contents for LI-COR LI-7500

  • Page 1 LI-7500 O Analyzer Instruction Manual ® Environmental Division...
  • Page 2 Open Path CO O Analyzer Instruction Manual...
  • Page 4 The information contained in this document is subject to change without notice. LI-COR MAKES NO WARRANTY OF ANY KIND WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. LI-COR shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material.

  • Page 5: Table Of Contents

    Table of Contents Section 1. Introduction Overview of the LI-7500 ................................Getting Started Tutorial ................................Section 2. Theory of Operation Relating Absorptance to Concentration............................Measuring Absorptance ................................Cross Sensitivity ................................... Zero Drift ...................................... Equation Summary ..................................LI-7500 Implementation ................................A Note About Pressure and Temperature ............................. 2-11...
  • Page 6 Mounting the Control Box ..............................Mounting the Sensor Head ..............................Serial Cable Connection ................................6-Pin Eurofast Serial Cable ..............................LI-7500 Serial Adapter Cable ............................... Standard Serial Cable ................................DAC Cable Connection ................................Installing the PC Communications Software on Your Computer ....................3-10 Operation - Using the LI7500 Software ............................
  • Page 7 Operational Considerations ................................3-50 Section 4. Calibration Introduction....................................How Stable are Zero and Span? ..............................Checking the Zero - Considerations ............................. Checking the Span - Considerations ............................. What Actually Happens................................Complete Step-by-Step Calibration Instructions .......................... Section 5. Maintenance Cleaning the Optical Path ................................Changing the Fuse ..................................
  • Page 8 Section 6. Troubleshooting Power On Problems ..................................PC Connection Problems................................Bad Temperature or Pressure Readings ............................Bad CO or H O Readings ................................Diagnostic Messages ..................................LI7500 Error Messages ................................Appendix A. Specifications Appendix B. Pin Assignments Appendix C. List of Suppliers Appendix D.

  • Page 9: Section 1. Introduction

    Introduction Overview of the LI-7500 The LI-7500 is a high performance, non-dispersive, open path infrared CO O analyzer designed for use in eddy covariance flux measurement systems. Some of the LI-7500's important features include: Simultaneous measurements of CO and H O in the free atmosphere.
  • Page 10 LI-7500 for your application, please contact LI-COR. If you have just taken delivery of your LI-7500, check the packing list to verify that you have received everything that was ordered and that you have also received the following items: Standard Spare Parts Kit - (part #9975-007).
  • Page 11 Section 1 Power Cable - (part #392-05619). 4m cable used to connect the LI-7500 to your 10.5- 30VDC power supply. SDM Interface Cable - (part #392-05618). Used to connect the LI-7500 in a Synchronous Device for Measurement (SDM) loop, such as those used by Campbell Scientific data recording devices.

  • Page 12: Getting Started Tutorial

    Keep this sheet in case you need to re-enter these values. Getting Started Tutorial The following section briefly covers the basic steps you might follow to set up the LI-7500 to collect and record data. Many of these steps are described in greater detail elsewhere in this manual.
  • Page 13 Figure 1-1. Align the marks and insert the cable connector. Connect the Power Supply The power supply cable (#392-05619) has a circular connector that attaches to the LI-7500 control unit front panel at the location shown in Figure 1-2. The other end has bare wire leads for connection to a 10.5-30VDC supply (2A or greater).
  • Page 14 Section 3, Installing the PC Communications Software on Your Computer. Connect the RS-232 Cables For convenience when operating the LI-7500 in the laboratory, a short adapter cable (#9975- 015) is provided for connecting the instrument to your computer.
  • Page 15 Section 1 Unplugged Internal RS-232 Connector 9975-015 Serial Adapter Cable Power Supply Adapter Cable Plug in here Connector Figure 1-2. Unplug the internal RS-232 connector, and plug in the adapter cable. Introduction...
  • Page 16 Section 1 Start the LI-7500 Communications Program Open the LI7500 Windows Communications program. Choose the COM (serial) port to which the RS-232 cable (Step 4) is connected to the computer, select a baud rate, and click on Connect . After a few seconds, you should see "live" numbers on the display.
  • Page 17 O, if this is a new instrument. As the internal chemicals become depleted, these values will increase (when you re-zero). * If you find the span needs re-setting, it is possible that your CO (or H O) standards differ from LI-COR's. Introduction...

  • Page 18: Section 2. Theory Of Operation

    Theory of Operation Relating Absorption to Concentration The scaling law of Jaimeson et. al. (1963) shows the effect of pressure on infrared absorption. If the amount of absorber of some gas u (mol m ) and absorption in a band are related by some function h (), then ...
  • Page 19 Section 2 ) by introducing a path length λ, and We rewrite this in terms of number density (mol m = ρ λ. Substituting this into Equation 2-1, and solving for the number density ρ noting that u of gas i yields ...

  • Page 20: Measuring Absorptance

    Φ is transmitted radiant power in the absorption band with some concentration of gas i present, and Φ is the transmitted radiant power in the absorption band with zero concentration of i present. The LI-7500 approximates absorptance   α...

  • Page 21: Cross Sensitivity

     Note the zeroing term z and the span adjustment term S in Equation (2-7). Cross Sensitivity Because the LI-7500 uses one detector for measuring A , and A , (the absorbed and non-absorbed power for CO and H O, respectively), there is a slight cross-sensitivity between gases due to imperfections in the detector's frequency (time) response.

  • Page 22: Zero Drift

     Zero Drift Even though the detector and filters are temperature controlled in the LI-7500, the detector is subject to slight temperature drift as ambient temperature changes. This error is directly related to the detector cooler control voltage, which is measured, and thus provides a mechanism for a software "fine tuning".

  • Page 23: Equation Summary

    Section 2 Equation Summary In the atmosphere, the absorption of radiation by water vapor is not significantly influenced by any other gas, so the effective pressure for water vapor P is simply the total pressure P. 2-11 O absorptance α is (from Equations 2-8 and 2-10) ...
  • Page 24 H O. Since the concentration of H O is most variable, it must be accounted for in the equivalent pressure of P A method of doing this (LI-COR Application Note #116) is = P ψ (m 2-14 where ψ (m...
  • Page 25 Section 2 molar density ρ (mmol m ) is   α ρ   2-17   ec c The coefficients for the 5th order polynomial f ( ) are given on the calibration sheet. Theory of Operation...

  • Page 26: Li-7500 Implementation

    Section 2 LI-7500 Implementation Atmospheric pressure P (kPa) and temperature T (°C) are measured by sensors in the control box (Figure 2-1). Their values are displayed on the Calibrations page. Tubing connected to pressure transducer Thermistor Figure 2-1. Temperature thermistor and pressure sensor location in control box.
  • Page 27 Section 2 Table 2-1. Fundamental equations used in the LI-7500 calculations. Label Description Equation   O mmol/m O number density α 2-18     O g/m O mass density 2-19 1000 O mmol/mol O mole fraction WR T...

  • Page 28: A Note About Pressure And Temperature

    • K A Note About Pressure And Temperature Since the LI-7500 is calibrated for number density, temperature is not required for the calculation, and accurate pressure measurement is not needed either (Equations 2-18 and 2- 22). For example, a 5% error in pressure typically leads to a 1% error in density for CO .
  • Page 29 Section 2 and saturated), a 10 °C error in the temperature measurement would make less than a 0.01% error in the CO number density. When computing mole fraction, however, temperature and pressure do need to be known as accurately as possible. Here, errors in pressure and temperature are directly proportional to errors in mole fraction.

  • Page 30: Section 3. Setup And Operation

    Setup and Operation Installing the LI-7500 Mounting the Control Box Brackets are included that can be used to mount the control box using bolts or U-clamps to secure the box to a tripod or other post. There are holes in the four corners of the box, as well, that can be used to attach the box directly to a flat surface, if desired.
  • Page 31 Section 3 Top View LI-7500 Control Box Mounting Bracket Post U-bolt Socket Head Screws (4) Control Box Side View Figure 3-1. Attach mounting brackets to control box, and secure to mounting post. Setup and Operation...
  • Page 32 Section 3 There are some additional considerations that should be taken into account when locating the control box, including: The cable that connects to the sensor head is 3m in length; determine the height at which the sensor head will be mounted, and plan to mount the control box accordingly. The thermal properties of the control box are such that it is OK to place the box in direct sun.

  • Page 33: Mounting The Sensor Head

    Section 3 Mounting the Sensor Head The LI-7500 sensor head has a mounting post that can be used to mount the analyzer. The mount is threaded to accept standard 3/8-16 tripod screws (a 1/4-20 adapter is also included, which can be threaded into the mounting post). Mounting the sensor head at a slight angle from vertical (~10-15°) may also help prevent water droplets from remaining on the windows...

  • Page 34: Serial Cable Connection

    This 4m cable has a 6-pin circular connector that plugs into the 'Serial Interface' port on the LI-7500 control unit front panel. The other end has bare wire leads that can be soldered to a standard DB-9 female connector (not included) for direct connection to a computer. This cable is unterminated so that it can be inserted through a hole in a weatherproof box, for example, that contains the logging device.

  • Page 35: Li-7500 Serial Adapter Cable

    Gray White LI-7500 Serial Adapter Cable (PN 9975-015) The Serial Adapter Cable is used to connect to the internal RS-232 connector, located on the PC board, as shown in Figure 1-2. This cable can be used for "in the laboratory" convenience.

  • Page 36: Standard Serial Cable

    Section 3 Standard Serial Cable (PN 9975-016) This is a null modem cable that is used to interface with devices such as computers, serial printers, and terminals with 9-pin serial ports. If you want to interface to a device with a 25- pin serial port, then a 9-pin to 25-pin adapter (in the spares kit) must be used.
  • Page 37 6-Pin Eurofast Cable Serial Adapter Cable 9-Pin Female Connector Standard Serial Cable 9-Pin Male Connector 9-Pin Serial Port Standard Serial Cable 25-Pin Serial Port 9-Pin to 25-Pin Adapter Figure 3-3. Schematic diagram of typical LI-7500 RS-232 cable configurations. Setup and Operation...

  • Page 38: Dac Cable Connection

    DAC1 (brown) or DAC2 (blue) wire to the positive input on your device. There is also a Ready Out wire (gray) that goes high when the LI-7500 has finished its warm- up period. This can be connected to a digital input on your logging device to indicate when the LI-7500 is sending "good"...

  • Page 39: Installing The Pc Communications Software On Your Computer

    Programs. Choose LI7500 from the list of programs and click the Add/Remove button. Operation - Using the LI7500 Software Data from the LI-7500 can be transferred to a computer for analysis, printing or storage using the RS-232 interface. The LI-7500 RS-232 port is configured as Data Terminal Equipment (DTE) with no hardware handshaking, and is bi-directional, meaning information can be transferred both into and out of the LI-7500.

  • Page 40: Connect Page - Establishing Communications

    The Connect page is the area in which you select the communication parameters for connecting the LI-7500 to your computer. The serial (COM) port, baud rate, and data acquisition frequency (in Hz) are chosen in this page. Click on the...
  • Page 41 Section 3 3-12 Setup and Operation...

  • Page 42: Calibration Page - Setting The Zero And Span

    This is the update frequency to be used while the LI7500 program communicates with the LI-7500. Select from 1, 2, 5, 10, or 20 Hz, or enter your own value (≥ 0 and ≤ 20.0). Note that at 9600 baud, the maximum update frequency is 5 Hz; at 19200 baud, 10 Hz; and at 38400 baud, 20 Hz.
  • Page 43 Section 3 3-14 Setup and Operation...
  • Page 44 Section 3 The CO Page shows the time and date of the last zero and/or span calibration, and contains buttons to set the zero and span. There is also an entry field to set the target value for the span gas that is being used to set the span of the instrument.

  • Page 45: Cal Coefficients Page

    Section 3 Cal Coefficients Page The LI-7500 uses a fifth order polynomial for the CO calibration, and a third order polynomial for H O calibration. The Calibration Coefficients page displays these factory- determined calibration coefficients, as well as a factor for correcting CO measurements for band broadening due to the presence of water vapor, and a zero drift correction factor (Z).
  • Page 46 Section 3 Setup and Operation 3-17...

  • Page 47: Changing Sensor Heads

    Values to Update. Click on the Update Selected button to send these values to the LI-7500 for implementation. Click the Cancel All button to change any edited values in the window back to the state they were in before editing.
  • Page 48 Attach the sensor head to the control box. Connect to the computer, and establish communications. Go to the File menu and select "Open Configuration". Make sure "Calibration", "Cal Coeffs", and "Update LI-7500" are checked in the "Select" dialog, and click "Continue". Setup and Operation...
  • Page 49 Section 3 NOTE: In 2002, the design of the main circuit board was changed to accommodate temperature operations to -40 °C (instrument control box serial numbers 75B-0370 and higher). The new board revision can be identified by a green LED visible during operation (below).

  • Page 50: Inputs Page - Temperature, Pressure, And Auxiliary Inputs

    Section 3 Inputs Page - Temperature, Pressure, and Auxiliary Inputs Setup and Operation 3-21...
  • Page 51 Temperature and pressure values are required by this program for converting CO and H density to mole fraction. In addition, the LI-7500 needs a pressure value to compute CO O mole density, and a temperature value to do the band broadening correction for H...
  • Page 52 Use the temperature and pressure radio buttons to select the method for measuring these values. If you are using the auxiliary input, enter the values for the multipler (A) and offset (B). If you have updated user-entered values, you need to send them to the LI-7500 for implementation using the Update Selected button.
  • Page 53 Table 2-21. The LI-7500 auxiliary input is a 12-bit differential input. The input range is 0 to +4096 mV. Since the input is uni-polar (e.g. measures only positive signals) users should note the polarity of their sensor output signal when connecting to this input channel.
  • Page 54 The polynomial for the thermistor is coded in the instrument software and does not allow user to substitute another thermistor. In practice the LI-7500 does have two auxiliary inputs but only one input is available to the user for this reason.
  • Page 55 Section 3 Auxiliary Input Example: Suppose you have a custom temperature sensor that outputs a linear 0 to +5VDC signal. This signal represents a -40 °C to +60 °C temperature range. The LI7500 software allows you to enter the proportional multiplier (slope) and offset for this sensor. (Select the Temperature Aux Input radio button of the Inputs Tab to activate this selection).
  • Page 56 Section 3 Setup and Operation 3-27...

  • Page 57: Outputs Page - Setting Dac And Sdm Outputs

    Section 3 Notes about on-board temperature and pressure sensors The LI-7500 internal temperature sensor has an accuracy of ±0.2 °C over a range from 0-70 °C. However, since it is positioned inside the control box the sensor will experience artificial heating from various active electronic components on the circuit board.
  • Page 58 Section 3 Setup and Operation 3-29...
  • Page 59 R = 5V. Delay Time The output signal from the LI-7500 optical bench is sampled by a high-speed A/D converter and input into a Digital Signal Processor (DSP). This signal is processed digitally and gas densities are computed from it. There is a fixed delay in this process, and an additional user-...
  • Page 60 For example, suppose you are sampling the LI-7500 with a Campbell Scientific CR23X datalogger at 10 Hz (0.1 s). Setting the delay count of the LI-7500 to 17 yields a total delay of .297 seconds, which means the LI-7500 data will have a delay of 3 execution intervals (0.297 s/0.1 s), which the logger can allow for in synchronizing the data to the sonic anemometer or...
  • Page 61 Bandwidth (5, 10 or 20 Hz) determines the signal averaging done by the digital filter. To avoid aliasing (only a concern for co-spectra, not for fluxes), one should sample the LI-7500 at a frequency greater than or equal to 2 times the bandwidth. Thus, if you are sampling at 10 Hz, set Bandwidth to 5 Hz.
  • Page 62 Section 3 Actual concentration Measured concentration .707 Time Figure 3-4. Bandwidth = 1/oscillation period. Bandwidth is a useful indicator for characterizing real-world behavior in which there are fluctuating gas concentrations. Given a sinusoidal oscillation of concentration, the instrument's ability to measure the full oscillation amplitude diminishes as the oscillation frequency increases.
  • Page 63 (Instruction 189, see the datalogger or the LI-7500 manual published by Campbell Scientific). Parameter 3 in the SDM-LI7500 instruction defines what data are sent to the datalogger from the LI-7500. Parameter 3 can take on values between 0 and 6. See Table 3-1 for parameter 3 value definitions.
  • Page 64 Section 3 Mode Items Sent mmol/m O mmol/m absorptance O absorptance Pressure (kPa) Temperature (C) Aux channel (user units) Cooler signal (Volts) Diagnostic value (see below) Bandwidth (Hz) Delay interval mmol/m O mmol/m Pressure (kPa) mmol/m O mmol/m Pressure (kPa) Diagnostic Value (see page 3-33) Setup and Operation 3-35...

  • Page 65: Page - Setting Rs-232 Output

    Example: a value is 125 (01111101) indicates Chopper not ok, and AGC = 81% (1101 is 13, times 6.25) Any of the parameters on this page that are edited can be sent to the LI-7500 for implementation by selecting the appropriate check boxes under 'Values to Update', and then...
  • Page 66 Section 3 When the 'Configure RS232 Port of LI-7500 when disconnected from the PC' check box is selected, the fields on this page become active. The parameters selected under Output will be sent to the RS-232 port at the baud rate and frequency selected. Select Ndx to output an index value.
  • Page 67 Section 3 3-38 Setup and Operation...
  • Page 68 If you do not intend to use unattended RS-232 data output, simply leave the Configure RS232 Port of LI-7500 when disconnected from the PC check box unchecked. Under Options, you can choose whether or not to output labels with each data record, and whether to output diagnostic text records.

  • Page 69: Pc Logging Page - Choosing The Values To Log

    Section 3 PC Logging Page - Choosing the Values to Log The PC Logging Page is used to configure the data output parameters used while the LI7500 program is active. On this page you specify the destination file, information to appear in the file header, the type of delimiter to be used between data records, and the values to be logged.
  • Page 70 Section 3 Setup and Operation 3-41...

  • Page 71: Strip Charts Page

    Section 3 File Header The file header is output each time the Start button is pressed and can contain a time stamp (derived from the computer's system time), calibration zero and span values, and user-entered remarks. Destination Enter a file name for the output file; the extension .TXT will be added automatically (although no extension is required).
  • Page 72 Section 3 smooth scrolling refreshes the chart after each data point is added (after data run off the right edge of the chart), and coarse scrolling moves the chart approximately 1/2 page at a time. Setup and Operation 3-43...
  • Page 73 Section 3 When you have configured the strip chart parameters, press the button. The chart will Start appear at the top of the page. Press Pause to temporarily stop plotting; press Stop to quit plotting. To update any of the strip chart parameters you must first press Stop .

  • Page 74: Diagnostics Page

    Section 3 Diagnostics Page The Diagnostics page allows you to view the current operational state of the LI-7500, including values of CO and H O absorptance, optical bench properties, and the current analyzer configuration. See Section 6, Troubleshooting for more information about the diagnostic indicators.

  • Page 75: Menu Description

    Section 3 ‘Current Configuration’ parameters This window provides an alternative method of viewing (but not setting) the LI-7500 configuration status. Menu Description File Menu The File menu contains commands that allow you to open and save existing configuration files, and to exit the program.
  • Page 76 Section 3 After you have selected a configuration file and clicked Open, the Select dialog appears (below). Setup and Operation 3-47...
  • Page 77 This dialog allows you to select only certain portions of the configuration file to be opened (useful if you don’t want to overwrite some of your present settings in the LI-7500 software). For example, to select only the strip chart portion of a configuration file, check the ‘Strip Charts’...
  • Page 78 • Inputs • Outputs and RS-232 If any of the above items are checked, you can use the “Update LI-7500” check box to have these items sent to the LI-7500 as well. NOTE: If you leave “Update LI-7500” unchecked, the selected configuration items will still show up on the PC program’s windows, from where you can update the LI-7500 if...

  • Page 79: Operational Considerations

    Help Menu About displays a screen showing the current version number of the LI7500 software. Help Topics opens the LI-7500 Help file, where you can select from a list of help topics. Operational Considerations The LI-7500 can tolerate droplets on the windows to a certain extent; the AGC value will increase, but the calibration is unchanged.
  • Page 80 Section 3 Rain/Snow Flying droplets and flakes in the optical path will affect the performance of the LI-7500, even if the total light blockage is small enough that the AGC does not reach 100%. The reason is that the objects are moving, and if a droplet or flake is in the path for a sample measurment, but out of the path for a reference measurement (or vice versa), it will influence the resulting reading.
  • Page 81 Section 3 Figure 3-4. Typical strip chart trace taken during a light snow shower. The higher the bandwidth, the more pronounced this effect, since less averaging is done. 3-52 Setup and Operation...
  • Page 82 Section 3 Dust and Pollen The LI-7500 is quite tolerant of small particulates on the windows, as long as they are small, and spectrally neutral. Pollen is a problem because it is sticky and can accumulate, so monitor the AGC values and clean the windows as needed.

  • Page 83: Section 4. Calibration

    The zero and span adjustments are used to bring the LI-7500's actual response into line with its previously determined factory response, at least at two points. It is the user's responsibility to do this step at regular intervals (weekly or monthly).

  • Page 84: How Stable Are Zero And Span

    Section 4 How Stable are Zero and Span? The analyzer's zero is primarily affected by temperature, and the state of the internal chemicals. The internal chemicals should be changed annually (see Section 5, Maintenance). The zero's response to temperature is relatively small (typically 0.1 or 0.2 ppm per °C for , or 0.01 mmol/mol/°C for H O).

  • Page 85: Checking The Zero - Considerations

    Section 4 Checking the Zero - Considerations The zero is checked with dry CO -free air within the optical path of the analyzer. A suitable source of air for setting the zero can be generated with chemical scrubbers (such as soda lime ®...

  • Page 86: What Actually Happens

    What Actually Happens In the LI-7500, the zero and span parameters are set in software via the serial port using a personal computer (see Section 3). What actually happens when the zero is set is that the...
  • Page 87 Section 4 − Similarly, − When the span is set, the value of S (or S for water) is determined. For example, if there is density ρ' a known CO in the optical path, then from Equation 2-17,   α...
  • Page 88 Section 4  ρ  −1     α ρ is given by 2-16. In terms of a known mole fraction m' , instead of a known density,   −1     P RT α If the CO concentration is dry, then P = P, so...

  • Page 89: Complete Step-By-Step Calibration Instructions

    Run the program (see Section 3). Then select the Calibration tab in the Main Window of the 7500-50 Communications software. Place the calibration tube into the sensor head as shown in Figure 4-1 and connect the temperature sensor cable to the LI-7500 control box. Calibration...
  • Page 90 Section 4 Calibration Tube (insert this end first) Thermistor Air Out Pressure (optional) Air In Figure 4-1. Flow calibration gas at the Air In port shown. Calibration...
  • Page 91 Section 4 Insert the top of the fixture first, and slide the bottom into place. It is very important that the fixture is centered between the windows covering the source and detector modules. It can be helpful to click on the Diagnostics tab in the 7500-50 software, and view the AGC value while centering the fixture;...
  • Page 92 Section 4 Note this value Figure 4-2. Note value of Z , shown as Current Value. When the reading has stabilized, click to set the CO zero. After a brief delay, the Zero displayed CO value should be fluctuating around zero. Check the resultant value of Z shown on the Zero CO page (Figure 4-2).
  • Page 93 Section 4 Click Zero. Note the new value of Z (typically between 0.65 and 0.85). Span CO Flow a CO span gas through the calibration tube at 0.5 to 1 liter/minute. Click on the CO Cal tab. Enter the mole fraction in the target entry. When stable (1-2 minutes) click .

  • Page 94: Section 5. Maintenance

    Maintenance Cleaning the Optical Path The LI-7500 optical windows should be cleaned when necessary (when the AGC value approaches 100%). If the windows become dirty it may become difficult to calibrate the analyzer. Excessive zero drift may also be observed if the optical path becomes obstructed.
  • Page 95 Section 5 The LI-7500 sensor head shown below in Figure 5-1 is from a long term test on a roof top on a snowy day (January 2001) in Lincoln, NE. Note the small puddle of water on the sapphire window; the AGC value was at 100%.

  • Page 96: Changing The Fuse

    Section 5 Changing the Fuse The LI-7500 power supply is protected by a 5A 250V, 5 × 20 mm fast-blow type fuse located on the main circuit board inside the control unit case (Figure 5-2). If the battery or other power source fails to power the LI-7500, check to see if the fuse has blown.

  • Page 97: Replacing The Internal Chemicals

    To check the fuse, power the unit off, disconnect the power to the unit, and open the case of the LI-7500 control unit. The fuse is located on the main circuit board, in the lower lefthand corner, as shown in Figure 5-2. Replacement fuses (part #439-04214, in the spares kit) plug into the fuse holder;...
  • Page 98 Section 5 Mounting Bracket Spacer Washer Remove these 2 screws Figure 5-3. Remove the 2 screws on the base of the mounting bracket. Maintenance...
  • Page 99 Section 5 Before removing the bottles, prepare the new bottles (in spares kit) by filling them with equal parts Ascarite II and magnesium perchlorate (Figure 5-4). Fill the bottles Filter Paper half full with Ascarite II first, followed by the magnesium perchlorate. Place a filter paper disk in the lid to keep the chemicals from spilling into the detector housing.
  • Page 100 Section 5 Side View Bottom View Soda Lime/Mg(ClO Insert 6-32 screw here to act as a knob for removal Soda Lime/Mg(ClO Remove the cover Bottle Covers (2) retention screw Figure 5-5. Remove the screw holding the bottle covers and replace the chemicals. Insert the recharged bottles into the analyzer housing cap first.
  • Page 101 H O zeros. Check the zero again, if possible, after one or two days. NOTE: LI-COR has written a publication that describes the use of chemical scrubbing agents with LI-COR gas analyzers. This publication, entitled "Using CO and H Scrubbers with LI-COR Gas Analyzers"...

  • Page 102: Section 6. Troubleshooting

    Troubleshooting Power On Problems The instrument requires between 10 and 30 VDC, at 2 Amps, to operate (a LI-COR LI-6020 battery charger, for example, will not by itself power the LI-7500). When adequate power is first applied to the instrument, the LED in the box near the fuse (Fig 5-1) will light up for about 5 seconds, then (if operating correctly) go off and remain off.

  • Page 103: Pc Connection Problems

    Make sure the LI-7500 is in fact powered and running (press the Reset button (Fig. 5-2) and see if the LED lights for about 5 seconds).

  • Page 104: Bad Temperature Or Pressure Readings

    (See "Note on Temperature and Pressure" on page 2-12). When setting the span of the LI-7500, however, it is important. If you know the pressure better than the LI-7500 does, then use the "User-Entered" option and enter it.

  • Page 105: Bad Co Or H O Readings

    H O Readings Section 2 details what the LI-7500 measures, and how it computes. Most of the relevant parameters are available for viewing with the LI7500 program, such as calibration coefficients, absorptances, and zero and span values. The first thing to check when tracking down bad readings is to make sure all of the coefficients on the "Cal Coeffs"...

  • Page 106: Diagnostic Messages

    Check the calibration coefficients and band broadening value (if the problem is with ) to make sure they are correct. Diagnostic Messages The Diagnostics page allows you to view the current operational state of the LI-7500, including values of CO and H O absorptance, optical bench properties, and the current analyzer configuration.
  • Page 107 Section 6 Troubleshooting...
  • Page 108 +50 and -25 °C. Sync Flag - If not OK, indicates that the LI-7500 embedded software and the digital signal processor (DSP) receiving the signal from the chopper motor in the sensor head are out of sync.
  • Page 109 This will typically be at -30 °C or below. AGC - Note this value when you first operate the LI-7500. Typical values are 50-60%. As dirt accumulates on the sensor head windows the value of AGC will increase, so you can use this value to indicate when it is necessary to clean the windows.

  • Page 110: Li7500 Error Messages

    Error Message Description The file was opened but could not be sent to the LI-7500. An error occurred when transmitting the file to the LI-7500. Not being connected is the most probable cause. Please enter a positive floating point value.
  • Page 111 Error Message Description A confirmation for your last action was not received. Results Each action or update sent to the LI-7500 requires an are questionable. acknowledgement. One was not received for your last action. It is unknown if the action was successful or not.

  • Page 112: Appendix A. Specifications

    Specifications* Type: Absolute, open-path, non-dispersive infrared gas analyzer. Detector: Thermo-electrically cooled lead selenide. Bandwidth: 5, 10, or 20 Hz, software selectable. Path Length: 12.5 cm (4.72"). Operating Temperature Range: -25 to 50°C (-40 to 50 °C verification test available on request). ®...
  • Page 113 Appendix A Control Box: 35 cm × 30 cm × 15 cm (external dimensions). IRGA cable: 3 meters (between sensor head and electronics control box). Power, Serial, DAC, Auxiliary Input and SDM cables: 4 meters Weight: Head: 0.75 kg (1.65 lb.), Control Box and Cables: 4.8 kg (10.5 lb.) µmol mol -3†...
  • Page 114 Pin Assignments Power Serial Interface SDM Interface DAC Outputs Auxiliary Inputs The sensor head is connected to two terminal strips at the upper righthand corner of the main circuit board, underneath the protective cover. Under normal circumstances you will not need to alter any of the sensor head connections. If, however, any of the wires should pull loose, refer to the diagram below for proper wiring connections.
  • Page 115 Appendix B Green/White & Orange Yellow & Blue/White Yellow/White & Orange/White Gray/White & Violet/White Black/White Brown/White Gray Black White Brown Blue Green Violet Red/White Shield Appendix B...
  • Page 116 Suppliers The company names, addresses, and phone numbers are the most current we have at the time of this printing. In some cases the information may change without notice. Soda Lime (6-12 mesh) and Magnesium Perchlorate (Anhydrous) Mg(ClO GFS Chemicals Soda Lime: Part #66352 P.O.
  • Page 117 Appendix C Fisher Scientific Soda Lime: Part #S201-212 711 Forbes Avenue (LI-COR Part #9960-071) Pittsburgh, PA 15219-4785 Phone: 201-467-6400 Mg(ClO : Part #M54-500 (500g) FAX: 201-379-7415 Toll free: 800-776-7000 Toll free FAX: 800-926-1166 www.fishersci.com Thomas Scientific Soda Lime: Part #C703-B76 P.O.
  • Page 118 Appendix C Ascarite II (8-20 mesh) Fisher Scientific MAX17731 711 Forbes Avenue 8-20 Mesh Pittsburgh, PA 15219-4785 Phone: 201-467-6400 FAX: 201-379-7415 Toll free: 800-776-7000 Toll free FAX: 800-926-1166 www.fishersci.com Thomas Scientific C049H40 P.O. Box 99 8-20 Mesh Swedesboro, NJ 08085-6099 Phone: 609-467-2000 FAX: 609-467-3087 Toll free: 800-345-2100...
  • Page 119 Eurofast® and Microfast® Cables (see Table C-1) Turck Inc. 3000 Campus Drive Minneapolis, MN 55441 Phone: 612-553-7300 FAX: 612-553-0708 www.turck.com Table C-1. Eurofast® and Microfast® cables used to connect to the LI-7500. LI-COR Part Number LI-7500 Control Box Cable Connector Turck Part Number Connector Type...
  • Page 120 Commands sent to the LI-7500 have a certain structure that must be followed, and data sent by the LI-7500 comes packaged in a particular way. For example, to set the Bandwidth to 10Hz, the following string (Outputs(BW 10)) should be sent followed by a line feed character (decimal 10).
  • Page 121 Outputs (BW 10 )) and so is this The LI-7500 does not try parsing a command string until a line feed is received. Since "extra" characters are ignored, commands can be terminated with carriage return and line feeds equally as well.
  • Page 122 (outputs(bw 10)) Who Sends What Not all of the commands in the LI-7500’s grammar are really commands. Some are designed to be used by the LI-7500 to package outgoing data. The command, or record, (Data..) might look like this (Data (CO2D 2.2083146e1)(H2OD 3.5485935e2)(Temp 2.5886261e1)(Pres...

  • Page 123: Command Summary

    Appendix D parse or recognize, and the record acknowledges a configuration change. It is also (Ack..) used to pass back the new zero or span setting after a command. (Calibrate..) Command Summary In the following sections, some abbreviations are used: {int} means an integer value, such as 0, 10, 452, etc.
  • Page 124 Appendix D The (Outputs..) Command is used to configure the items pertaining to data output, including the (Outputs..) bandwidth, delay time, DACs (digital to analog convertors), and the RS-232 port. The actual RS-232 output uses the record described in Table 2. (Data..) Table 1: The Outputs Command Command...
  • Page 125 Appendix D Command Subcommands Remarks Baud rate for RS-232 (Baud 9600 | 19200 | 38400 {float}) Output frequency of (Data..) records in Hz. (Freq Usable values: 0.0 thru 20.0 {bool}) (Pres {bool}) (Temp {bool}) (Outputs (RS232 (Aux {bool}) These commands determine what is included (CO2Raw in the (Data output record {bool})
  • Page 126 Appendix D (EOL "{hex code(s)"}) End of Line character. Enter hex value in double quotes. Example: (Outputs(RS232(EOL "0D0A)))lf would terminate data strings with a carriage return and a line feed. (Ndx {bool}) Determines whether an index value is transmitted or not. Example: (Outputs(RS232(Ndx TRUE)))lf would cause the data stream to contain an index value.
  • Page 127 The following are several examples of data formatting. The command string sent to the LI- 7500 is terminated with a line feed character. EXAMPLE (Labels TRUE) Data format Transmitted to LI-7500 (Outputs(RS232(Freq 1)(EOL "0D0A")(Ndx TRUE)(DiagRec FALSE)(DiagVal TRUE)(Labels TRUE)))lf Received from LI-7500...
  • Page 128 Appendix D (Data (Ndx 1545)(DiagVal 250)(CO2Raw 1.5386712e-1)(CO2D 3.2183277e1)(H2ORaw 3.57 75542e-2)(H2OD 1.9687008e2)(Temp 2.4227569e1)(Pres 9.8640356e1)(Aux 0)(Cooler 1.5756724)) (Data (Ndx 1809)(DiagVal 250)(CO2Raw 1.5380490e-1)(CO2D 3.2162146e1)(H2ORaw 3.57 57541e-2)(H2OD 1.9677452e2)(Temp 2.4227569e1)(Pres 9.8543587e1)(Aux 0)(Cooler 1.5750400)) Appendix D...
  • Page 129 Notice how this format is much cleaner and reduces the overhead of redundant label transmissions. The data selected for output data record is accomplished with the (Outputs(RS232(CO2Raw TRUE)...))command. Transmitted to LI-7500 (Outputs(RS232(Freq 1)(EOL "0D0A")(Ndx TRUE)(DiagRec FALSE)(DiagVal TRUE)(Labels FALSE)))lf Received from LI-7500 0.15401 32.2167 0.03569 196.703 24.33...
  • Page 130 Appendix D Example (Labels TRUE) Value Example CO2Raw 1.5388799e-1 CO2D 3.2176308e1 H2OD 1.9711704e2 Temp 2.4171295e1 Pres 9.8543587e1 Cooler 1.5700240 LABELS FALSE Value Floating Point Example CO2Raw, H2ORaw, Aux x.xxxxx 0.12345 CO2D xx.xxxx 15.1234 H2OD xxx.xxx 354.123 Cooler x.xxxx 1.1234 Temp xx.xx 24.35 Press...
  • Page 131 Example variable length ~ -2E8 to +2E8 Diag. Examples: To set the LI-7500 to output only CO and H O molar densities once every 2 seconds: (Outputs(RS232(Freq .5)(Pres FALSE)(Temp FALSE)(Aux FALSE)(CO2Raw FALSE)(CO2D TRUE)(H2ORaw FALSE)(H2OD TRUE)(Cooler FALSE))) To configure DAC #1 to output CO...
  • Page 132 Appendix D Data and Status Records records are the vehicles with which the LI-7500 outputs (Data..) (Diagnostics..) data through its RS-232 port. The frequency with which it outputs records is deter- (Data..) mined by the command, shown in Table 1. Data and status (Outputs(RS232(Freq..)))
  • Page 133 Appendix D Table 2: Data and Diagnostics Records Record Subcommands Remarks {int}) Index value. Boolean controlled output. Increments every 6.5 ms (1/ 152). Resets to 0 whenever the configuration changes, or (with no changes) about every 163 days. {float}) Temperature, °C Temp {float}) Pressure, kPa...
  • Page 134 Sent by the LI-7500 to aknowledge any incoming command. Received TRUE {float}) Only sent after zeroing and spanning commands. Contains the new, computed value of zero or span. Sent by the LI-7500 when it cannot parse or recognize a Error (Received TRUE command. {quoted Version string}) Output by the LI-7500 during synchronization.
  • Page 135 (Outputs (RS232 (Freq 0)(DiagRec FALSE)))lf The LI-7500 also supports toggling of the Clear To Send (CTS) line to request a data record. This hardware polling would be normally used when the update frequency is set to 0 as described above.
  • Page 136 Appendix D the LI-7500 to transmit a data record. The length of time that CTS must be held low is very short ( ~50 microseconds). Users familiar with programming RS232 interfaces may already understand that RS-232 logic TRUE (1) is considered a low (or negative) voltage and logic FALSE (0) is considered a high (or positive) voltage.
  • Page 137 Data Set Ready Input Request To Send Output Clear To Send Input Ring Indicator Input A possible wiring configuration using the LI-COR RS-232 cable, part #392-05620 to a computer would be: LI-COR CABLE DB9 ON HOST COMPUTER Color Function Function Black...
  • Page 138 Appendix D Note about Embedded Software RS-232 Communication Priorities The RS-232 hardware and software trigger does not tap directly into the same data stream that is output to the DAC's and the SDM. The trigger actually sends a request to the data router task in the DSP to output a single data record over the RS-232 port.
  • Page 139 Appendix D The (Inputs..) Command command is used to scale the Auxiliary input channel, and to determine how (Inputs..) pressure and temperature are measured by the LI-7500. Table 3: The Inputs Command Command Subcommands Remarks (Source { Aux | Measured |...
  • Page 140 Appendix D (Inputs(Aux(A 10)(B 0))(Temperature(Source Aux))) To measure pressure and temperature normally, using the built-in sensors, send this: (Inputs(Pressure(Source Measured))(Temperature(Source Measured))) The (Calibrate..) and (Coeffs..) Commands commands control zeroing, spanning, and factory (Calibrate..) (Coeffs..) calibration coefficients. The (Date subcommand must be present, and (Val must be absent to perform (ZeroH2O and (ZeroCO2.
  • Page 141 (ZeroH2O {quoted string}) Date The date field triggers the (ZeroCO2 LI-7500 to do a zero immedi- ately. The new value will be returned in an ( ..) record. (Calibrate {float}) For setting the span directly. If not present will trigger a calibration.
  • Page 142 Command Subcommands Remark {quoted string}) The 75H-xxxx head number. (SerialNo {float})) The band broadening coeffi- (Band (A cient (1.15 for the LI-7500). (A {float}) (B {float}) (C {float}) (D {float}) (CO2 (E {float}) These values are found on the (Coeffs...
  • Page 143 To force the H O channel to use the value 0.96 for its zero, send this: (Calibrate(ZeroH2O(Val 0.96))) To make the LI-7500 set its CO span right now, with 400 µmol†mol flowing through the calibration tube, first compute the target density using Equation 2-24 (solved for C). If the temperature is 23°C, and the pressure 98kPa, then the mode density is 15.92 mmol...
  • Page 144 Appendix D The Program Reset Command is the equivalent of pressing the reset button on the main board. It (Program(Reset TRUE)) is generally only used to access lower level software for updating the embedded program, or when the instrument is not responding normally. Table 5: Synchronization Commands Command Remarks...
  • Page 145 Appendix D The Query Command The Query (?) command is used to query the LI-7500 for any configuration parameter individually, as well as any node in the configuration tree. Table 6: Query Commands Command Remarks The query for individual parameters...
  • Page 146 Appendix D (H2OD TRUE)(Ndx TRUE)(DiagVal TRUE)(DiagRec TRUE)(Labels TRUE)(EOL "0a"))) whereas the query (Outputs(RS232(Freq ?)))lf would respond: (Freq 5) (Calibrate ?)lf causes a Calibrate record to be put in the output queue. Example Response: (Calibrate (ZeroH2O (Val 9.9986296e-1)(Date "Aug 29 2000 at 1:43:59 PM"))(ZeroCO 2 (Val 1.3099210)(Date "Aug 29 2000 at 4:26:54 PM"))(SpanH2O (Val 9.8932171e-1)(...
  • Page 147 Appendix D 997e-3)(Z 6.7999997e-3)(A 4.5109792e3)(B 2.9099099e6)(C 8.9501600e7))(Band (A 1. 1499999)))) (Outputs ?)lf causes a Outputs record to be put in the output queue. Example Response: (Outputs (BW 10)(Delay 0)(SDM (Address 7))(Dac1 (Source NONE)(Zero -5e- 2)(Full 4 e-1))(Dac2 (Source PRESSURE)(Zero -1e-1)(Full 4e-1))(RS232 (Baud 38400)(Freq 0)( Pres TRUE)(Temp TRUE)(Aux TRUE)(Cooler TRUE)(CO2Raw TRUE)(CO2D TRUE)(H2ORaw TRUE...
  • Page 148 (Diagnostics (SYNC TRUE)(PLL TRUE)(DetOK TRUE)(Chopper TRUE)(Path 65)) (EmbeddedSW ?)lf causes an EmbeddedSW record to be put in the output queue. Example Response: (EmbeddedSW (Model "LI-7500 CO2/H2O Analyzer Application")(Version "2.0") ) (Inputs ?)lf causes an Inputs record to be put in the output queue. Example Response: (Inputs (Pressure (Source Measured)(UserVal 9.8000002e1))(Temperature...
  • Page 149 Appendix D Instrument Reset If the reset button is pressed, or a break condition was transmitted, the following commands will not change from their previous state: (Outputs (RS232 (EOL <bool>) (DiagRec <bool>) (Ndx <bool>)(Labels <bool>)(DiagVal <bool>) LI7500 Windows Program Extensions The LI7500 Windows program extends the configuration grammar to store various settings used by the program but not the instrument.
  • Page 150 Appendix D Table 7: LI7500 Windows Program Extensions (Continued) Command Subcommands Remarks {quoted string}) Strip chart left variable {float}) Left axis max value LMax {float}) Left axis min value Lmin {quoted string}) Strip chart right variable {float}) Right axis max value (Chart Rmax {float})
  • Page 151 Appendix D Command Subcommands Remarks Baud { 9600 | 19200 | 38400 {float}) Value between 0 and 20.0 Connect Freq {int}) Value between 1 and 38. Port {bool }) Include cal information? {bool }) Which delimiter? Space {bool }) { quoted string }) Log file name Name {bool })
  • Page 152 Appendix D Command Subcommands Remarks {bool }) Cooler voltage (V) {bool }) absorption Cabs {bool }) mmol m Cden {bool }) mg m CdenMg {bool }) µmol mol {bool }) O Dew point (°C) {bool }) O absorptance LogVals Habs {bool }) O mmol m Hden...
  • Page 153 The purpose of this section is to describe the protocol used to establish communications with the LI-7500 when it is operating in an “unknown” mode. That is, when the baud rate is not known, nor are any other details about the instrument’s configuration.
  • Page 154 Appendix D The host can then send the desired configuration changes, if any, to the LI-7500. If the configuration change involves a baud rate change, the LI-7500 will send its ( record before changing baud rates. A typical configuration dump as generated by the above protocol is shown below.
  • Page 155 ® LI-COR, inc. Environmental Division 4421 Superior Street P.O. Box 4425 Lincoln, Nebraska 68504 USA Phone: 402-467-3576 FAX: 402-467-2819 Toll-free 1-800-447-3576 (U.S. & Canada) E-mail: envsales@env.licor.com Internet: http://www.licor.com...

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