SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES

FIGURE 7.4-1. Thermocouples with External Reference Junction

In the following example, an external temperature measurement is used as the reference for 5 thermocouple measurements. A Campbell Scientific 107 Temperature Probe is used to measure the reference temperature. The connection scheme is shown in Figure 7.4-1.

If a more accurate reference temperature is needed, Campbell Scientific's TCR6 utilizes a 100 ohm PRT to measure the reference temperature and provides better insulation for a more isothermal reference.

The temperature (°C) of the 107 Probe is stored in Input Location 1 and the thermocouple temperatures (°C) in Locations 2-6.

PROGRAM

01:P11 Temp 107 Probe

01:

1

Rep

02:

11

IN Chan

03:1 Excite all reps w/EXchan 1

04:1 Loc [:REF TEMP ]

05:

1

Mult

06:

0

Offset

02:P14 Thermocouple Temp (DIFF)

01:

5

Reps

02:22 7.5 mV 60 Hz rejection Range

03:

1

IN Chan

04:1 Type T (Copper-

Constantan)

05:1 Ref Temp Loc REF TEMP

06:

2

Loc [:TC #1 ]

07:

1

Mult

08:

0

Offset

7.5 107 TEMPERATURE PROBE

Instruction 11 excites Campbell Scientific's 107 Thermistor Probe (or the thermistor portion of the 207 temperature and relative humidity 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).

PROGRAM

01:P11 Temp 107 Probe

01:

3

Reps

02:

1

IN Chan

03:1 Excite all reps w/EXchan 1

04:1 Loc [:107 T #1 ]

05:

1

Mult

06:

0

Offset

7.6207 TEMPERATURE AND RH PROBE

Instruction 12 excites and measures the RH portion of the Campbell Scientific 207 Temperature and Relative Humidity probe. This instruction relies on a previously measured temperature (°C) to compute RH from the probe resistance. Instruction 11 is used to obtain the

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