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Fluke 7381 User Manual

Calibration bath
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7381
Calibration Bath
User's Guide
June 2013, Rev. 1, 5/23 (English)
©2013-2023 Fluke Corporation. All rights reserved.
Specifications are subject to change without notice.
All product names are trademarks of their respective companies.

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  • Page 1 7381 Calibration Bath User’s Guide June 2013, Rev. 1, 5/23 (English) ©2013-2023 Fluke Corporation. All rights reserved. Specifications are subject to change without notice. All product names are trademarks of their respective companies.
  • Page 2 Fluke authorized resellers shall extend this warranty on new and unused products to end-user customers only but have no authority to extend a greater or different warranty on behalf of Fluke. Warranty support is available only if product is purchased through a Fluke authorized sales outlet or Buyer has paid the applicable international price.

  • Page 3: Table Of Contents

    Table of Contents Title Page Introduction....................Contact Fluke Calibration ................Safety Information ..................Specifications and Environmental Conditions ........... Installation ....................Unpack the Product ................Uncrate and Move the Bath ..............Bath Environment ................. Tipping Prevention Bracket Installation ..........Installation On A Wood Floor ............
  • Page 4 7381 User’s Guide Water ....................18 Ethylene Glycol ................18 Mineral Oil..................18 Silicone Oil ..................18 Fluid Characteristics Charts............. 19 Stirring ....................23 Heater ....................23 Temperature Controller................. 23 Cutout ....................23 Cooling Control..................24 Refrigeration....................24 Controller Operation .................. 26 Bath Temperature.................
  • Page 5 Calibration Bath CTO ....................41 BO and BG..................41 H and L .................... 41 HGbt....................41 Digital Communication Interface..............42 Serial Communications................. 42 Wiring....................42 Interface Commands ................43 Calibration Procedure................47 Calibration Points.................. 47 Measure the Set-point Error ..............48 Compute R and ALPHA ..............
  • Page 6 7381 User’s Guide...

  • Page 7: Introduction

    +1-425-446-5500 info@flukecal.com Safety Information General safety Information is in the printed 7381 Safety Information document that ships with the Product. It can also be found online at www.flukecal.com. More specific safety information is listed in this manual where applicable.
  • Page 8 7381 User’s Guide A Warning identifies conditions and procedures that are dangerous to the user. A Caution identifies conditions and procedures that can cause damage to the Product or the equipment under test. W Caution • The drain valve on the back of the Bath must be closed before you attempt to fill the tank with fluid.

  • Page 9: Specifications And Environmental Conditions

    Turning the Product on and off frequently adds wear to the compressor. Bath or compressor lifetime can be affected by turning the Product off and on frequently. Fluke Calibration recommends to turn the bath off if it is not going to be used for the weekend or an extended period of time.

  • Page 10: Unpack The Product

    • 2019-DCB Kit, Liquid-in-Glass (LIG) Adapter and Carousel (optional) • 2069 Scope, Liquid-in-Glass (LIG) with mounts (optional) If missing any item, contact Fluke Calibration. See Contact Fluke Calibration. Uncrate and Move the Bath When you uncrate the Bath, remove all of the accessories from the foam around the Bath and remove the foam.

  • Page 11: Bath Environment

    Bath completely into the bracket caster slots, Figure 1. Lock the front casters. Gently push on the Bath to make sure that it is securely locked into the tipping bracket. If you have questions about the installation, contact Fluke Calibration. Installation On A Wood Floor The wood floor installation kit includes lag bolts.
  • Page 12 7381 User’s Guide Figure 1. Tipping Prevention Bracket Installation Front Caster Slots Wall 21.6 cm (8.5”)

  • Page 13: Parts And Controls

    Calibration Bath Parts and Controls Parts and Controls Front Panel The front-panel controls and indicators are shown in Table Table 1. Front Panel Number Description Control indicator light - A two-color LED that indicates the ratio of heating to cooling. •...

  • Page 14: Bath Tank And Lid

    Drill or cut holes in the cover to accommodate the instruments calibrated or immersed in the Bath. Spare covers are available from Fluke Calibration. • A stainless steel baffle inside the tank ensures proper fluid flow and protects probes and thermometers from contact with the stirrers.

  • Page 15: Rear Panel And The Fluid Expansion Reservoir

    Calibration Bath Parts and Controls Rear Panel and the Fluid Expansion Reservoir Access these items from the rear panel: • Systems fuses • Power cord • High/low voltage indicator • Drain • Serial port, IEEE-488 port (if installed) • Fluid expansion reservoir Attached to the Bath rear panel is the fluid expansion reservoir.

  • Page 16: Before You Begin

    7381 User’s Guide Caution To prevent Product damage, know that the overflow tube is not large enough to handle large flow rates encountered from an over-filled tank. The tube is for expanding fluid rates from heating only. Fill only until the level reaches the top of...
  • Page 17 Calibration Bath Before You Begin Caution To avoid Product damage, make sure the immersion coils are completely covered when you fill the tank. Do not fill above the stir baffle, see Figure Figure 2. Stir Baffle Fill Level Maximum Fill Level Top of Baffle Minimum Fill MIN FILL...

  • Page 18: Power

    If necessary, cover the panel while you fill the Bath. Do not overfill. The Bath does not come with bath fluid. Various fluids are available from Fluke Calibration or other sources. Depending on the desired temperature range, any of the fluids below, or others, can be used: •...

  • Page 19: Set The Temperature

    Calibration Bath Bath Use Caution To avoid Product damage, do not turn on the Bath without fluid in the tank. Make sure the heating coils are fully immersed. Rear Panel and the Fluid Expansion Reservoir. Fill the Bath with clean, unpolluted fluid. Fill the Bath carefully through the large rectangular access hole to a level that allows for stirring and thermal expansion, see Thermal Expansion.

  • Page 20: Comparison Calibration

    Bath work area. Nevertheless, insert the probes to the same depth in the bath fluid. Make sure to insert all probes deep enough to prevent stem effect. Fluke Calibration recommends a general rule for immersion depth to reduce the stem effect to a minimum: 20 x the diameter of the DUT + the sensor length.

  • Page 21: Calibrate Multiple Probes

    Calibration Bath General Operation Calibrate Multiple Probes Fully loading the Bath with probes increases the temperature stabilization time after you insert the probes. Use the reference probe as the guide and make sure that the temperature is stable before you start calibration. General Operation The information in this section is for general information only.

  • Page 22: Thermal Conductivity

    7381 User’s Guide Thermal Conductivity Thermal conductivity measures how easily heat flows through the fluid. Thermal conductivity of the fluid affects the control stability, temperature uniformity, and temperature settling time. Fluids with higher conductivity distribute heat quicker, more evenly, and improves Bath performance.

  • Page 23: Electrical Resistivity

    Calibration Bath General Operation = 9.2 / [0.00077 (300-25) + 1] = 7.59 inches (18.98 cm) Electrical Resistivity Electrical resistivity is how well the fluid insulates against electric current flow. In some applications, such as when you measure the resistance of bare temperature sensors, it can be important that little or no electrical leakage occur through the fluid.

  • Page 24: Water

    At higher temperatures, vapor emission becomes significant. The vapors can be dangerous and Fluke Calibration highly recommends the use of a fume hood or adequate ventilation. As with most oils, mineral oil expands as temperature increases, see...

  • Page 25: Fluid Characteristics Charts

    The fluid information given in this manual is intended only as a general guide to choose a fluid. Though every effort has been made to provide correct information, Fluke Calibration cannot guarantee accuracy of data or assure suitability of a fluid for a particular application.
  • Page 26 7381 User’s Guide Table 2. Table of Bath Fluids Lower Thermal Thermal Resistivity Upper Temp. Flash Viscosity Specific Specific Heat Fluid Temp. Conductivity Expansion Limit* Point (centistokes) Gravity (cal/g/°C) Ω-cm) Limit* (cal/s/cm/°C) (cm/cm/°C) Halocarbon 5.7 @ –50 °C –100 °C 70 °C (e)
  • Page 27 In the graph, it is assumed that the bath access hole is covered at this point. This is subject to you company policy. Fluke Calibration recommends the use of a ventilation system as soon as the fluid produces vapors. Keep the access hole covered to reduce evaporation.
  • Page 28 7381 User’s Guide Figure 3. Chart Showing Usable Range of Various Fluids...

  • Page 29: Stirring

    Calibration Bath General Operation Stirring Stirring of the bath fluid is important for stable temperature control. The fluid must be mixed well for good temperature uniformity and fast controller response. The stirrer is precisely adjusted for optimum performance. Heater The temperature controller precisely controls the Bath heater to maintain a constant bath temperature.

  • Page 30: Cooling Control

    7381 User’s Guide If the cutout is activated because of excessive bath temperature, power to the heater shuts off, the bath cools, and the display flashes Cut-out . The display flashes between the actual temperature and Cut-out until the temperature falls below the reset temperature and the cutout is reset.
  • Page 31 The refrigeration can be beneficially used for short times (<1 hr) >60 °C but <100 °C. This list is not complete, but suggests some situations when automatic modes might not be best. Fluke Calibration recommends use of the automatic functions as they are adequate.

  • Page 32: Controller Operation

    7381 User’s Guide Controller Operation This section discusses Bath temperature controller operation with the front control panel. Use the front panel to: • monitor the Bath temperature • set the temperature set-point in degrees C or F • monitor the heater output power •...
  • Page 33 Calibration Bath Controller Operation Figure 4. Controller Operation Flowchart SET + Display Program Menu EXIT Temperature Number of Set-points EXIT Reset Cutout Adjust Set-point Select Set-point Cutout Active EXIT Select Setpoint EXIT Soak Time SECONDARY FUNCTIONS EXIT Adjust Setpoint EXIT Program Function Mode Display Power EXIT...

  • Page 34: Temperature Set-Point

    7381 User’s Guide Temperature Set-point The Bath temperature can be set to any value within the range as given in the specifications with a high degree of resolution. The temperature range of the particular bath fluid must be known by the operator and the Bath should only be operated well below the upper temperature limit of the fluid.

  • Page 35: Set-Point Vernier

    Calibration Bath Controller Operation Set-point Vernier Use the set-point vernier to adjust the temperature below or above the set-point by a small amount with high resolution. Each of the eight stored set-points has an associated vernier setting. The set-point vernier can be set in increments of 0.00018 °C. To access the vernier from the set-point: 1.

  • Page 36: Temperature Scale Units

    7381 User’s Guide Temperature Scale Units Set the temperature scale units to degrees Celsius (°C) or Fahrenheit (°F). The Bath shows these units for: • bath temperature • set-point • vernier • proportional band • cutout set-point Access the temperature units after the vernier adjustment function.

  • Page 37: Set-Points

    Calibration Bath Controller Operation Set-points The next parameters are the program set-points. For example: 1 50. 0 First set-point 1. Use the UP or DOWN buttons to select any of the set-points. For example, set-point 3: 3 30. 0 Third set-point 2.

  • Page 38: Program Control

    7381 User’s Guide Program Control The final menu item is the control parameter. These options are available to control the ramp and soak program: • Start the program from the beginning ( • Continue the program from where it was when it was stopped ( Cont •...

  • Page 39: Proportional Band

    Calibration Bath Controller Operation Proportional Band In a proportional controller like this, heater output power is proportional to the Bath temperature over a limited range of temperatures around the set-point. This temperature range is the proportional band. At the bottom of the proportional band, heater output is 100 %. At the top of the proportional band, heater output is 0 %.

  • Page 40: Cutout Set-Point

    7381 User’s Guide The proportional band should also be wider when fluid viscosity is higher because of the increased response time. Easily adjust the proportional band width from the front panel. You can set the width to discrete values in the selected temperature units. Monitor the stability with a high-resolution thermometer or with the controller percent output power display to determine the optimum proportional band width setting.

  • Page 41: Controller Configuration

    Calibration Bath Controller Operation CO= 110C Cutout set-point 1. Push UP or DOWN to change the cutout set-point. DOWN Decrement display CO= 75C New cutout set-point 2. Push SET to accept the new cutout set-point. The next function is the configuration menu. Push EXIT to show the Bath temperature. Controller Configuration Configuration and operating options and calibration parameters follow the cutout set-point function in the secondary menu.

  • Page 42: Operating Parameters

    7381 User’s Guide Operating Parameters When in the probe menu, push UP to indicate the operating parameters menu ( Push SET to enter the menu. The operating parameters menu contains: • cooling mode • hot gas bypass mode Cooling Mode...
  • Page 43 Calibration Bath Controller Operation The HGb ( ) modes are: • Auto (normally-set mode) • On (manual) • If for a special application, the automatic mode is undesirable, set the HGb to On or Off. Automatic Mode: This mode is best for most applications. When you scan down in temperature (for set points >2 °C below the current temperature) the system switches to maximum cooling capacity.

  • Page 44: Serial Interface Parameters

    7381 User’s Guide 4. Push UP or DOWN to change the value. HGb Po HGB setting parameter indicator 5. Push SET to access the parameter setting Current HGb setting value 6. Push UP or DOWN to change the value (if in On mode).

  • Page 45: Sample Period

    Calibration Bath Controller Operation Sample Period Sample period is the next parameter in the Serial Interface Parameter menu. The sample period is the time, in seconds, between temperature measurements transmitted from the serial interface. If you set the sample rate ( SAnPLE ) to 5, the Bath transmits the current measurement over the serial interface approximately every 5 seconds.

  • Page 46: Ieee-488 Setup (Optional)

    7381 User’s Guide Setup IEEE-488 (Optional) Baths can be fitted with an IEEE-488 GPIB interface option. To use the IEEE-488 interface, connect an IEEE-488 standard cable to the back of the Bath, set the device address, and set the transmission termination character.

  • Page 47: Calibration Parameters

    H and L The factory-set parameters, H and L ( ), set the upper and lower set-point limits of the Bath. Note Fluke Calibration recommends a high limit setting below the flash-point of the fluid in the Bath. HGbt Caution To ensure best performance without damage to the Bath compressor, do not alter this parameter value.

  • Page 48: Digital Communication Interface

    7381 User’s Guide Digital Communication Interface The Bath can communicate with and be controlled by other equipment through the digital interface. An RS-232 serial interface which is standard and an IEEE-488 GPIB interface is optional. See Serial Interface Parameters IEEE-488 Setup (Optional).

  • Page 49: Interface Commands

    Calibration Bath Digital Communication Interface Figure 6. Serial Communication Cable Wiring Interface Commands The various commands to access the Bath controller functions from the digital interfaces are in Table 5. Use the commands with the RS-232 serial interface and the IEEE-488 GPIB interface. Commands are terminated with a carriage-return character (Cr, ASCII 13).
  • Page 50 7381 User’s Guide Table 5. Interface Command Summary Command Command Returned Acceptable Command Description Returned Format Example Example Values Display Temperature Read current set-point s[etpoint] set: 9999.99 {C or F} set: 150.00 C s[etpoint]=n s=150 Instrument Range Set current set-point to n...
  • Page 51 Calibration Bath Digital Communication Interface Table 5. Interface Command Summary (cont.) Command Returned Acceptable Command Description Command Format Returned Example Example Values Secondary Menu Read proportional band setting pr[op-band] pb: 9.999 pb: 0.315 Depends on Set proportional band to n pr[op-band]=n pr=0.326 Configuration...
  • Page 52 7381 User’s Guide Table 5. Interface Command Summary (cont.) Command Returned Acceptable Command Description Command Format Returned Example Example Values Calibration Menu Read C0 calibration parameter b0: 9.9999 b0: 0.0002 Set C0 calibration parameter to *b0=n *b0=0 Unlimited Read CG calibration parameter bg: 999.99...

  • Page 53: Calibration Procedure

    Calibration Bath Calibration Procedure Calibration Procedure Note Consider this procedure a general guideline. Each laboratory should write their own procedure based on their equipment and their quality program. Each procedure should have an uncertainty analysis based on the laboratory equipment and environment. In some instances, you may want to calibrate the Bath to improve the temperature set-point accuracy.

  • Page 54: Measure The Set-Point Error

    7381 User’s Guide Measure the Set-point Error The first step in the calibration procedure is to measure the temperature errors (including sign) at the two chosen calibration temperatures. 1. Set the Bath to the lower set-point, t 2. Wait for the Bath to reach the set-point and allow 15 minutes to stabilize at that temperature.

  • Page 55: Calibration Example

    Calibration Bath Calibration Procedure Calibration Example The Bath is to be used between 25 °C and 75 °C and it is desired to calibrate the Bath as accurately as possible for operation within this range. The current values for R and ALPHA are 100.000 and 0.0038500, respectively.

  • Page 56: Maintenance

    Before you use another cleaning or decontamination method, except those recommended, check with a Fluke Calibration service center to make sure that the proposed method does not damage the equipment, see Contact Fluke Calibration.
  • Page 57 Calibration Bath Maintenance • Check the fluid at least every month for the first year and regularly thereafter. This fluid check provides a baseline for knowledge of Bath operation with clean, usable fluid. Once some fluids are compromised, fluid break down can occur rapidly. Pay particular attention to the viscosity of the fluid.

  • Page 58: Troubleshooting

    If a problem arises, read this section carefully and attempt to understand and solve the problem. If the probe seems faulty or the problem cannot otherwise be solved, contact Fluke Calibration for assistance. Make sure to have the model number and serial number of your Product available.
  • Page 59 Report of Test are accurate. Cycle the power off, disconnect the bath from ac, and then restart the Bath. • If the problem reoccurs, replace the battery. Contact Fluke Calibration for assistance. The display flashes Cut-out and an •...
  • Page 60 100 Ω to 300 Ω value between pins 1 and 4 depending on the temperature. If the probe is defective, contact Fluke Calibration. • If the problem is not the probe, erroneous data in memory can be the cause. Re-initialize the memory...
  • Page 61 The display flashes Cut- and an incorrect process temperature. • Make sure that the control probe has not been struck, bent, or damaged. If the cause of the problem remains unknown, contact Fluke Calibration.
  • Page 62 4. If the display shows InIt and/or the cycle count shows a low number, such as 0002, the battery is spent and needs replacement. Contact Fluke Calibration. 5. After the battery is replaced, you must reprogram the calibration and user-adjustable parameters into the controller.
  • Page 63 • Intermittent shorts in the heater or controller electronic circuitry can also be a possible cause. Contact Fluke Calibration. Too much heating or not enough cooling can cause this problem. Check that the control indicator glows green which The Bath does not achieve low shows that the controller is attempting to cool.
  • Page 64 7381 User’s Guide...

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