A. VOLTAGETOTEMPERATURE CONVERSION
When SCM7B37 thermocouple modules are used to measure temperature, the measured output voltage must often be converted back to temperature. This is readily
done with the SCM7B37 series because Cold Junction Compensation (CJC) is incorporated into the module and SCM7B backpanels.
The conversion method is illustrated with an example:
A type K thermocouple (TC) is to be used with the SCM7B37K02:
 Identify the TC and Module Voltage ranges:
Temperature Input

Module Voltage Output

100°C 
+1V 
+1350°C 
+5V 
The Minus Full Scale Module Output (known as the "Pedestal") = +1V
The Module V_{OUT} Range is 5 1 = 4V
 From the type K TC tables determine the full scale voltages:
V(100°C) = 3.5531mV (TC Neg. F.S. Voltage)
V(+1350°C) = +54.138mV (TC Pos. F.S. Voltage)
TC V_{IN} Range = TC Pos. F.S. Voltage TC Neg. F.S. Voltage
The SCM7B37K module gain (G), is given by:
G = Module VOUT Range / TC VIN Range
∴G = (4) / [0.054138 (0.0035531)] = 69.335 V/V
3. C
 Calculate the effective TC voltage (V_{T}) from the Measured Module Output Voltage (V_{OUT}) using the following formula:
SCM7B37 Module Output VoltagetoThermoelectric Voltage
Equation 1:
V_{T} = [(V_{OUT} Pedestal) / G] + (TC Neg. F.S. Voltage)
∴V
_{T} = (Module Measured V
_{OUT} 1V) / 69.335) + (0.003553)
 Find the value of the field temperature being measured by crossing V_{T}
to thermocouple temperature in your application programs thermocouple looktable
(referenced to a 0°C CJC temperature, which is the case as long as the thermocouplebackpanel junction is within the specified CJC ambient range).
SCM7B37 Module values used in Equation 1 are shown in the following table. ITS90 characteristics were used to calculate.
Module type

G (V/V)

PEDESTAL, V

Thermocouple Neg.Full Scale (mV)

SCM7B37J01 
84.120 
+1 
4.6325 
SCM7B37J01A 
105.150 
0 
4.6325 
SCM7B37J01D 
210.300 
0 
4.6325 
SCM7B37J10 
371.101 
+1 
0.0 
SCM7B37J10A 
463.876 
0 
0.0 
SCM7B37J10D 
927.752 
0 
0.0 
SCM7B37J11 
183.083 
+1 
0.0 
SCM7B37J11A 
228.853 
0 
0.0 
SCM7B37J11D 
457.707 
0 
0.0 
SCM7B37J12 
120.837 
+1 
0.0 
AN701: Continued
Module type

G (V/V)

PEDESTAL, V

Thermocouple Neg.Full Scale (mV)

SCM7B37J12A 
151.046 
0 
0.0 
SCM7B37J12D 
302.093 
0 
0.0 
SCM7B37J13 
238.447 
+1 
+16.3272 
SCM7B37J13A 
298.059 
0 
+16.3272 
SCM7B37J13D 
596.118 
0 
+16.3272 
SCM7B37K02 
69.335 
+1 
3.5531 
SCM7B37K02A 
86.669 
0 
3.5531 
SCM7B37K02D 
173.338 
0 
3.5531 
SCM7B37K20 
327.639 
+1 
0.0 
SCM7B37K20A 
409.549 
0 
0.0 
SCM7B37K20D 
819.097 
0 
0.0 
SCM7B37K21 
160.607 
+1 
0.0 
SCM7B37K21A 
200.759 
0 
0.0 
SCM7B37K21D 
401.518 
0 
0.0 
SCM7B37K22 
81.903 
+1 
0.0 
SCM7B37K22A 
102.379 
0 
0.0 
SCM7B37K22D 
204.758 
0 
0.0 
SCM7B37K23 
167.135 
+1 
+24.9055 
SCM7B37K23A 
208.919 
0 
+24.9055 
SCM7B37K23D 
417.837 
0 
+24.9055 
SCM7B37T03 
164.945 
+1 
3.3786 
SCM7B37T03A 
206.181 
0 
3.3786 
SCM7B37T03D 
412.362 
0 
3.3786 
SCM7B37E04 
58.151 
+1 
0.0 
SCM7B37E04A 
72.689 
0 
0.0 
SCM7B37E04D 
145.377 
0 
0.0 
SCM7B37R05 
191.598 
+1 
0.0 
SCM7B37R05A 
239.497 
0 
0.0 
SCM7B37R05D 
478.994 
0 
0.0 
SCM7B37S06 
216.177 
+1 
0.0 
SCM7B37S06A 
270.221 
0 
0.0 
SCM7B37S06D 
540.441 
0 
0.0 
SCM7B37B07 
294.331 
+1 
0.0 
SCM7B37B07A 
367.914 
0 
0.0 
SCM7B37B07D 
735.828 
0 
0.0 
When the SCM7B47 thermocouple modules are used to measure temperature, the measured output voltage is also often converted back to temperature.
This is readily done with the SCM7B47 series because, like the SCM7B37 Modules, Cold Junction Compensation (CJC) is incorporated into the module and
SCM7B backpanels. However, unlike the SCM7B37 Modules, the module output voltage is a linear representation (Y = M X + B) of the input temperature.
The conversion method is illustrated with an example.
A type T thermocouple (TC) is to be used with the SCM7B47T06.
 Determine the Module Transfer Function:
Temperature Input

Module Voltage Output

100°C 
+1V 
+200°C 
+5V 
Let T_{LOW} ≡ Neg. Full Scale Temperature = 100°C
Let M ≡ (Output Voltage Span)/(Input Temp Span) = +13.333mV / °C
 Find the Temperature corresponding to Module Output Voltage:
Since Y = MX + B, with X = (Field Temperature T_{LOW})
V_{OUT} = M x (Field Temperature T_{LOW}) + Pedestal
Solving for the Field Temperature gives:
SCM7B47 VoltagetoTemperature Conversion
Equation 2:
Temperature = (V_{OUT} Pedestal) / M + T_{LOW}
with
M = (Module Output Volt Span) / (Input Temp Span)
In this case, Temperature (°C) = (V_{OUT} 1V) / 13.333mV + (100°C)
AN701: Continued
SCM7B47 Module values used in Equation 2 are shown in the following table:
Module type

M (mV/°C)

Pedestal, V

T_{LOW}, °C

SCM7B47J01 
5.2632 
+1 
0 
SCM7B47J01A 
6.5790 
0 
0 
SCM7B47J01D 
13.1579 
0 
0 
SCM7B47J02 
10.0000 
+1 
100 
SCM7B47J02A 
12.5000 
0 
100 
SCM7B47J02D 
25.0000 
0 
100 
SCM7B47K03 
3.0769 
+1 
0 
SCM7B47K03A 
3.8462 
0 
0 
SCM7B47K03D 
7.6923 
0 
0 
SCM7B47K04 
6.6667 
+1 
0 
SCM7B47K04A 
8.3333 
0 
0 
SCM7B47K04D 
16.6667 
0 
0 
SCM7B47T05 
10.0000 
+1 
0 
SCM7B47T05A 
12.5000 
0 
0 
SCM7B47T05D 
25.0000 
0 
0 
SCM7B47T06 
13.3333 
+1 
100 
SCM7B47T06A 
16.6667 
0 
100 
SCM7B37J12A 
33.3333 
0 
100 
SCM7B47E07 
4.4444 
+1 
0 
SCM7B47E07A 
5.5555 
0 
0 
SCM7B47E07D 
11.1111 
0 
0 
SCM7B47R08 
3.2000 
+1 
+500 
SCM7B47R08A 
4.0000 
0 
+500 
SCM7B47R08D 
8.0000 
0 
+500 
SCM7B47S09 
3.8095 
+1 
+700 
SCM7B47S09A 
4.7619 
0 
+700 
SCM7B47S09D 
9.5238 
0 
+700 
SCM7B47B10 
4.0000 
+1 
+800 
SCM7B47B10A 
5.0000 
0 
+800 
SCM7B47B10D 
10.0000 
0 
+800 
SCM7B47N11 
3.6364 
+1 
+200 
SCM7B47N11A 
4.5455 
0 
+200 
SCM7B47N11D 
9.0909 
0 
+200 
B. COLD JUNCTION COMPENSATION (CJC)
A negative temperature coefficient Thermistor is used as the SCM7B CJC sense element in a voltage divider configuration. It is mounted underneath each field side
terminal block. A nonlinear current is used to develop a linear voltage potential which is input to the modules X+
input pin. This potential changes over temperature.
Inside the module, this slope is modified to match the thermocouple type's Seebeck Coefficient (at+25°C) which offsets the effect of the thermocouple to backplane
junction potential. Thus, the module highlevel output potential is the field Thermocouple temperature and NOT the difference between the field temperature and
backpanel temperature.
This Thermistor is manufactured by BetaTHERM, P/N 100K6A1 (other manufacturers of acceptable replacements are listed in the Other Part Numbers of Interest
at end of the SCM7B catalog section).
The Thermistor is rated at 100kΩ at +25°C, ±0.2°C from 0°C to +70°C. For temperatures other than +25°C, the SteinhartHart Equation can be used with coefficients
provided by the Thermistor manufacturer.
STEINHARTHART EQUATION
Equation 3:
1/T = A + Bln(R) + C[ln(R)]^{3}
Where T is in Kelvin, Thermistor Resistance (R) in Ohms, and coefficients A,B,C are given by:
A = 8.27153E04
B = 2.08796E04 (per BetaTHERM for model 100K6A1)
C = 8.060985E08
To convert to °C, simply subtract 273.15 from the Kelvin temperature result.