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SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES
This section gives some examples of Input Programming for common sensors used with the CR510.
These examples detail only the connections, Input, Program Control, and Processing Instructions
necessary to perform measurements and store the data in engineering units in Input Storage. Output
Processing Instructions are omitted (see Section 8 for some processing and program control examples).
It is left to the user to program the necessary instructions to obtain the final data in the form desired. No
output to final storage will take place without additional programming.
The examples given in this section would likely be only fragments of larger programs. In general, the
examples are written with the measurements made by the lowest numbered channels, the instructions at
the beginning of the program table, and low number Input Storage Locations used to store the data. It is
unlikely that an application and CR510 configuration exactly duplicates that assumed in an example.
These examples are not meant to be used verbatim; sensor calibration, input channels, and input
locations must be adjusted for the actual circumstances. Unless otherwise noted, all excitation channels
are switched analog output.
7.1 SINGLE ENDED VOLTAGE
107 TEMPERATURE PROBE
Instruction 11 excites Campbell Scientific's 107
Thermistor Probe with a 2 VAC excitation, makes a
single ended measurement and calculates
temperature ( C) with a fifth order polynomial. In this
example, the temperatures are obtained from three
107 probes. The measurements are made on single-
ended channels 1-3 and the temperatures are stored in
Input Locations 1-3.
CONNECTIONS
The black leads from the probes go to
excitation channel 1, the purple leads go to
analog ground (AG), the clear leads go to
ground (G), and the red leads go to single-
ended channels 1, 2, and 3 (channel 1H,
channel 1L, and channel 2H, respectively).
01:
Temp (107) (P11)
1:
3
2:
1
3:
1
4:
1
5:
1
6:
0
7.2 DIFFERENTIAL VOLTAGE
MEASUREMENT
Some sensors either contain or require active
signal conditioning circuitry to provide an easily
measured analog voltage output. Generally, the
PROGRAM
Reps
SE Channel
Excite all reps w/E1
Loc [ 107_T_1 ]
Mult
Offset
output is referenced to the sensor ground. The
associated current drain usually requires a
power source external to the CR510. A typical
connection scheme where AC power is not
available and both the CR510 and sensor are
powered by an external battery is shown in
Figure 7.2-1. Since a single-ended
measurement is referenced to the CR510
ground, any voltage difference between the
sensor ground and CR510 ground becomes a
measurement error. A differential measurement
avoids this error by measuring the signal
between the 2 leads without reference to ground.
This example analyzes the potential error on a
differential CO
measurement using a LI-COR
2
CO
/H
O analyzer, model LI-6262.
2
2
The wire used to supply power from the external
battery is 18 AWG with an average resistance of
6.5 ohms/1000 ft. The power leads to the CR510
and LI-6262 are 2 ft and 10 ft, respectively.
Typical current drain for the LI-6262 is 1000 mA.
When making measurements, the CR510 draws
about 35 mA. Since voltage is equal to current
multiplied by resistance (V=IR), ground voltages
at the LI-6262 and the CR510 relative to battery
ground are:
LI-6262 ground =
1A
6.5 ohms/1000 ft
CR510 ground =
0.035A
6.5 ohms/1000 ft
10 ft = +0.065 V
2 ft = +0.0005 V
7-1
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