Campbell Scientific CR10TCR User Manual

INSTRUCTION MANUAL

CR10TCR

Thermocouple Reference

Revision: 12/96

Copyright (c) 1995-1996

Campbell Scientific, Inc.

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CR10TCR Table of Contents

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1. General........................................................................1

1.1 Specifications............................................................................................1

2. Accuracy — Temperature Sensor .............................1

3. Installation and Wiri ng ...............................................2

4. Programming ..............................................................2

5. Instruction 11 Details..................................................2

6. Electrically Noisy Environments ...............................3

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CR10TCR THERMOCOUPLE REFERENCE

1. GENERAL

The Model CR10TCR Probe contains a
thermistor for measuring temperature and is
used as a reference temperature for
thermocouples measured with the CR10. It is
installed between the two terminal stripes in the
wiring panel. After all the thermocouples are
wired, the wiring panel cover is installed to
minimize temperature gradients on the terminal
strip.

1.1 SPECIFICATIONS

Temperature Measurement Range: -35° to +50°C
Thermistor Interchangeability Error: Typically

<±0.2°C over 0°C to 60°C ±0.4 @ -35°C.
Polynomial Linearization Error: <±0.5°C over

-35°C to +50°C.

2. ACCURACY − TEMPERATURE
SENSOR

The overall probe accuracy is a combination of
the thermistor's interchangeability specification,
the precision of the bridge resistors, and the
polynomial error. In a "worst case" all errors

add to an accuracy of ±0.4°C over the range of

-24° to 48°C and ±0.9°C over the range of

-38°C to 53°C. The major error component is
the interchangeability specification of the
thermistor, tabulated in Table 1. For the range
of 0° to 50°C the interchangeability error is
predominantly offset. The bridge resistors are

0.1% tolerance with a 10 ppm temperature
coefficient. Polynomial errors are tabulated in
Table 2 and plotted in Figure 1.

TABLE 1. Thermistor Interchangeability

Specification

Temperature

Temperature (°C) Tolerance (

−40 0.40

−30 0.40

−20 0.32

−10 0.25

0 to +50 0.20

TABLE 2. Polynomial Error

-40 to +56 <±1.0°C

-38 to +53 <±0.5°C

-24 to +48 <±0.1°C

±°C)

FIGURE 1. Error Produced by Polynomial Fit to Published Values

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CR10TCR THERMOCOUPLE REFERENCE

)

3. INSTALLATION AND WIRING

The wiring diagram for the CR10TCR is shown
in Figure 1. The probe requires a single-ended
analog input channel and an excitation channel.
After the CR10TCR and thermocouple are
connected to the datalogger, install the wiring
panel cover (Figure 2 and 3).

Analog
Ground; Clear

Single-Ended Input; Red (1H

FIGURE 2. Wiring Diagram

Switched
Excitation;
Black (E3)

0.0 yields temperature in Celsius. For Fahrenheit,
use a multiplier of 1.8 and an offset of 32.

CAUTION: The reference temperature for
thermocouples must be in degrees Celsius.

EXAMPLE 1. Sample CR10 Instructions

01: P11 Temp 107 Probe

01: 1 Rep
02: 1 IN Chan
03: 3 Excite all reps w/EXchan 3
04: 15* Loc [:Ref_Temp]
05: 1 Mult
06: 0 Offset

* Proper entries will vary with program and
input location.

5. INSTRUCTION 11 DETAILS

Understanding the details in this section are not
necessary for general operation of the CR10TCR
with Campbell Scientific's dataloggers.

Instruction 11 outputs a precise 2 VAC excitation and
measures the voltage drop due to the sensor
resistance (Figure 5). The thermistor resistance
changes with temperature. Instruction 11 calculates
the ratio of voltage measured to excitation voltage
(Vs/Vx) which is related to resistance, as shown below:

FIGURE 3. Wiring Panel, CR10TCR, and

Wiring Panel Cover

FIGURE 4. CR10TCR Installed on the CR10

Wiring Panel

4. PROGRAMMING

Instruction 11 is used to measure the CR10TCR.
Instruction 11 provides AC excitation, makes a
single ended voltage measurement, and
calculates temperature with a fifth order
polynomial. A multiplier of 1.0 and an offset of

Vs/Vx = 1000/(Rs+249000+1000)
where Rs is the resistance of the thermistor.
See the measurement section of the datalogger

manual for more information on bridge
measurements.

Instruction 11 then calculates temperature using a
fifth order polynomial equation correlating Vs/Vx with
temperature. The polynomial coefficients are given
in Table 3. The polynomial input is (Vs/Vx)*800.

Resistance and datalogger output at several
temperatures are shown in Table 4.

Black

Red

Clear

FIGURE 5. CR10TCR Reference Temperature

Schematics

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CR10TCR THERMOCOUPLE REFERENCE

TABLE 3. Temperature, Resistance, and

Datalogger Output

Temperature Resistance Output

°COHMS°C

-40.00 4067212 -39.18

-38.00 3543286 -37.55

-36.00 3092416 -35.83

-34.00 2703671 -34.02

-32.00 2367900 -32.13

-30.00 2077394 -30.18

-28.00 1825568 -28.19

-26.00 1606911 -26.15

-24.00 1416745 -24.11

-22.00 1251079 -22.05

-20.00 1106485 -20.00

-18.00 980100 -17.97

-16.00 869458 -15.95

-14.00 772463 -13.96

-12.00 687276 -11.97

-10.00 612366 -10.00

-8.00 546376 -8.02

-6.00 488178 -6.05

-4.00 436773 -4.06

-2.00 391294 -2.07

0.00 351017 -0.06

2.00 315288 1.96

4.00 283558 3.99

6.00 255337 6.02

8.00 230210 8.04

10.00 207807 10.06

12.00 187803 12.07

14.00 169924 14.06

16.00 153923 16.05

18.00 139588 18.02

20.00 126729 19.99

22.00 115179 21.97

24.00 104796 23.95

26.00 95449 25.94

28.00 87026 27.93

30.00 79428 29.95

32.00 72567 31.97

34.00 66365 33.99

36.00 60752 36.02

38.00 55668 38.05

40.00 51058 40.07

42.00 46873 42.07

44.00 43071 44.05

46.00 39613 46.00

48.00 36465 47.91

50.00 33598 49.77

52.00 30983 51.59

54.00 28595 53.35

56.00 26413 55.05

58.00 24419 56.70

60.00 22593 58.28

TABLE 4. Polynomial Coefficients

Coefficient Value

C0 -53.4601
C1 90.807
C2 -83.257
C3 52.283
C4 -16.723
C5 2.211

6. ELECTRICALLY NOISY ENVIRONMENTS

AC power lines can be the source of electrical
noise. If the datalogger is in an electronically
noisy environment, the CR10TCR temperature
measurement should be measured with the AC
half bridge (Instruction 5) with the 60 Hz rejection
integration option on the CR10 (see Section 13
of the datalogger manual for more information
on noise). Instruction 11's fast integration will
not reject 60 Hz noise.

Example 2. Sample CR10 Instructions Using

AC Half Bridge

01: P5 AC Half Bridge

01: 1 Rep
02: 22 7.5 mV 60 Hz rejection Range
03: 1 IN Chan
04: 3 Excite all reps w/EXchan 1
05: 2000 mV Excitation
06: 15* Loc [:Ref_Temp]
07: 800 Mult
08: 0 Offset

02: P55 Polynomial

01: 1 Rep
02: 1* X Loc Air Temp
03: 15* F(X) Loc [:Ref_Temp]
04: -53.46 C0
05: 90.807 C1
06: -83.257 C2
07: 52.283 C3
08: -16.723 C4
09: 2.211 C5

* Proper entries will vary with program and

input location assignments.

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CR10TCR THERMOCOUPLE REFERENCE

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