Making Radiometric Measurements with Thermopile Detectors

This article briefly shows how to make radiometric measurements using thermopile detectors. However, before taking measurements, the cold junction temperature of the thermopile has to be approximated. Dexter has included internally mounted thermistors on certain models as well as externally mounted thermistors on all of its models.

The DC-4005 Chip Thermistors can be internally mounted on all Dexter’s models such as the ST120, ST150, ST60, 2M, 2M Quad, 10-Channel, T34, TM34 and the SLA32 array to track the thermopile’s ambient temperature. Dexter supplies the DC-4007 Chip-in-Glass Thermistors that can be mounted externally by customers.

Customers can either supply thermistors to Dexter or select from the company’s regular range of thermistors. In addition, the ST60R and ST150R on detector die poly-silicon resistor/thermistors are also available.

Chip Thermistor DC-4005 (T4)

The key specifications of the Chip Thermistor DC-4005 (T4) (Dexter part number: DC-4005 (formerly MT04)) include:

Cornerstone Sensors P/N TC1005
Description 30kΩ 5% R/T Curve E chip thermistor
Resistance @ 25°C 30,000Ω
Tolerance on resistance @ 25°C +/-5%
Dimensions (width, length, thick) inches 0.027 x .027 x .010

Table 1. shows resistance versus temperature in 1°C increments, and Table 2 shows Curve E resistance versus temperature in 5°C increments.

Table 1. Resistance versus temperature in 1°C increments -- Curve E resistance at 25°C = 30,000Ω.

Resistance Resistance Resistance Resistance
(°C) (Ohms) (°C) (Ohms) (°C) (Ohms) (°C) (Ohms)
-50.0 1,692,966 0.0 94,980 50.0 10,969 100.0 2,070.0
-49.0 1,583,474 1.0 90,413 51.0 10,564 101.0 2,009.9
-48.0 1,481,706 2.0 86,090 52.0 10,177 102.0 1,951.8
-47.0 1,387,075 3.0 81,996 53.0 9,804.9 103.0 1,895.7
-46.0 1,299,040 4.0 78,119 54.0 9,448.7 104.0 1,841.4
-45.0 1,217,106 5.0 74,445 55.0 9,107.1 105.0 1,789.0
-44.0 1,140,816 6.0 70,964 56.0 8,779.5 106.0 1,738.2
-43.0 1,069,751 7.0 67,663 57.0 8,465.3 107.0 1,689.1
-42.0 1,003,525 8.0 64,534 58.0 8,163.8 108.0 1,641.7
-41.0 941,781 9.0 61,565 59.0 7,874.5 109.0 1,595.7
-40.0 884,192 10.0 58,749 60.0 7,596.8 110.0 1,551.3
-39.0 830,456 11.0 56,076 61.0 7,330.2 111.0 1,508.3
-38.0 780,295 12.0 53,538 62.0 7,074.3 112.0 1,466.6
-37.0 733,450 13.0 51,129 63.0 6,828.5 113.0 1,426.3
-36.0 689,686 14.0 48,841 64.0 6,592.5 114.0 1,387.3
-35.0 648,783 15.0 46,667 65.0 6,365.7 115.0 1,349.6
-34.0 610,539 16.0 44,600 66.0 6,147.8 116.0 1,313.0
-33.0 574,767 17.0 42,636 67.0 5,938.4 117.0 1,277.6
-32.0 541,293 18.0 40,769 68.0 5,737.0 118.0 1,243.2
-31.0 509,958 19.0 38,993 69.0 5,543.5 119.0 1,210.0
-30.0 480,614 20.0 37,303 70.0 5,357.4 120.0 1,177.8
-29.0 453,125 21.0 35,696 71.0 5,178.4 121.0 1,146.6
-28.0 427,362 22.0 34,165 72.0 5,006.3 122.0 1,116.3
-27.0 403,208 23.0 32,709 73.0 4,840.7 123.0 1,087.0
-26.0 380,555 24.0 31,321 74.0 4,681.3 124.0 1,058.6
-25.0 359,301 25.0 30,000 75.0 4,527.9 125.0 1,031.0
-24.0 339,353 26.0 28,741 76.0 4,380.3 126.0 1,004.3
-23.0 320,623 27.0 27,541 77.0 4,238.1 127.0 978.37
-22.0 303,031 28.0 26,398 78.0 4,101.2 128.0 953.23
-21.0 286,502 29.0 25,307 79.0 3,969.4 129.0 928.85
-20.0 270,966 30.0 24,268 80.0 3,842.4 130.0 905.20
-19.0 256,359 31.0 23,276 81.0 3,720.1 131.0 882.25
-18.0 242,619 32.0 22,329 82.0 3,602.2 132.0 859.97
-17.0 229,691 33.0 21,426 83.0 3,488.6 133.0 838.36
-16.0 217,523 34.0 20,564 84.0 3,379.1 134.0 817.38
-15.0 206,067 35.0 19,741 85.0 3,273.6 135.0 797.02
-14.0 195,276 36.0 18,955 86.0 3,171.8 136.0 777.24
-13.0 185,109 37.0 18,204 87.0 3,073.7 137.0 758.05
-12.0 175,527 38.0 17,487 88.0 2,979.0 138.0 739.40
-11.0 166,494 39.0 16,801 89.0 2,887.7 139.0 721.30
-10.0 157,974 40.0 16,146 90.0 2,799.6 140.0 703.71
-9.0 149,936 41.0 15,520 91.0 2,714.6 141.0 686.63
-8.0 142,351 42.0 14,920 92.0 2,632.5 142.0 670.03
-7.0 135,190 43.0 14,347 93.0 2,553.3 143.0 653.90
-6.0 128,428 44.0 13,799 94.0 2,476.9 144.0 638.23
-5.0 122,041 45.0 13,275 95.0 2,403.0 145.0 623.00
-4.0 116,005 46.0 12,773 96.0 2,331.7 146.0 608.20
-3.0 110,301 47.0 12,292 97.0 2,262.9 147.0 593.81
-2.0 104,907 48.0 11,832 98.0 2,196.4 148.0 579.82
-1.0 99,806 49.0 11,391 99.0 2,132.1 149.0
150.0
566.22
552.99

 

Table 2. Curve E resistance vs. temperature in 5°C Increments with manufacturing tolerance adders, resistance at 25°C = 30,000Ω ± 5%.

Temp. (°C) Resistance at Temp. (ohms) NTC (%/°C) Point Matched Resistance Mfg. Tolerance Adder (±%) Resistance Tolerance at Temp. (±%)
-50 1,692,966 -6.71 6.5 11.5
-45 1,217,106 -6.49 5.7 10.7
-40 884,193 -6.29 5.0 10.0
-35 648,783 -6.09 4.4 9.4
-30 480,615 -5.91 3.8 8.8
-25 359,301 -5.73 3.3 8.3
-20 270,966 -5.56 2.8 7.8
-15 206,067 -5.39 2.4 7.4
-10 157,974 -5.24 2.0 7.0
-5 122,041 -5.09 1.7 6.7
0 94,980 -4.94 1.4 6.4
5 74,445 -4.80 1.1 6.1
10 58,749 -4.67 0.8 5.8
15 46,667 -4.54 0.5 5.5
20 37,303 -4.42 0.3 5.3
25 30,000 -4.30 0.0 5.0
30 24,268 -4.18 0.3 5.3
35 19,741 -4.07 0.5 5.5
40 16,146 -3.97 0.7 5.7
45 13,275 -3.87 0.9 5.9
50 10,969 -3.77 1.2 6.2
55 9,107.1 -3.67 1.4 6.4
60 7,596.9 -3.58 1.6 6.6
65 6,365.7 -3.49 1.8 6.8
70 5,357.4 -3.41 2.0 7.0
75 4,527.9 -3.32 2.1 7.1
80 3,842.4 -3.24 2.3 7.3
85 3,273.6 -3.17 2.5 7.5
90 2,799.6 -3.09 2.7 7.7
95 2,403.0 -3.02 2.8 7.8
100 2,070.0 -2.95 3.0 8.0
105 1,788.9 -2.88 3.1 8.1
110 1,551.3 -2.82 3.3 8.3
115 1,349.7 -2.75 3.4 8.4
120 1,177.8 -2.69 3.6 8.6
125 1,031.1 -2.63 3.7 8.7
130 905.10 -2.57 3.9 8.9
135 797.10 -2.52 4.0 9.0
140 703.80 -2.46 4.2 9.2
145 623.10 -2.41 4.3 9.3
150 552.90 -2.36 4.5 9.5

Definitions of Terms Used

The negative temperature coefficient (NTC) of resistance refers to the percentage of the resistance change with respect to the change in temperature, and is represented in units of -%/°C. One way to establish the thermistor’s approximate % resistance tolerance at a specific temperature is to multiply the specified NTC value by the temperature tolerance at that particular temperature.

In the case of thermistors that have a specified tolerance at a single temperature point the tolerance at other temperature points is determined using the manufacturing tolerance. Generally, thermistors are specified at 25°C temperature. Also the manufacturing tolerance can be added to the given point matched tolerance to establish the resistance tolerance at a different temperature point.

For instance, a thermistor having a ± 5% resistance tolerance at 25°C temperature exhibits a ± 6.4% tolerance at 0°C temperature. Typically point matched thermistors should not continuously work over a temperature of 105°C.

Chip-in-Glass Thermistor DC-4007 (T6)

The key specifications of the Chip-in-Glass Thermistor DC-4007 (T6) (Dexter part number: DC-4007 (formerly MT06)) are as follows:

   
Thermometrics P/N GC32KB203
Description 20kΩ 5% B-curve Chip-in-Glass thermistor
Resistance @ 25°C 20,000Ω
Tolerance on resistance @ 25°C +/-5%
Resistance ratio (R0°C /R70°C ) 18.77
Dimensions (diameter, length) inches Φ.033 x .084

Figure 1 shows the resistance of the DC-4007 thermistor as a function of temperature.

DC-4007 resistance as a function of temperature

Figure 1. DC-4007 resistance as a function of temperature

Thermistor ST60R

The following are the key specifications of the ST60R thermistor (Dexter part number: ST60R):

Description 30kΩ 20% on detector die thermistor, poly-silicon curve 0.11%±.003%/°C [ ΔR/(R*ΔT)]
Resistance @ 23°C 30,000Ω
Tolerance on resistance @ 23°C +/-20%
Resistance ratio (R0°C /R70°C) 0.953
Dimensions inches NA`

 

Figure 2 shows the resistance of the ST60R thermistor as a function of temperature.

ST60R resistance as a function of temperature

Figure 2. ST60R resistance as a function of temperature

Thermistor ST150R

The following are the key specifications of the ST150R thermistor (Dexter part number: ST150R):

Description 75kΩ 20% on detector die thermistor, poly-silicon curve 0.11%±.003%/°C [ ΔR/(R*ΔT)]
Resistance @ 23°C 75,000Ω
Tolerance on resistance @ 23°C +/-20%
Resistance ratio (R0°C/R70°C ) 0.957
Dimensions inches NA

 

Figure 3 shows the resistance of the ST150R thermistor as a function of temperature.

ST150R resistance as a function of temperature

Figure 3. ST150R resistance as a function of temperature

This information has been sourced, reviewed and adapted from materials provided by Dexter Research.

For more information on this source, please visit Dexter Research.

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