OM-WEB Series User's Guide
Specifications
35
Thermistor measurement accuracy
Table 7. Thermistor measurement accuracy specifications
Thermistor
Sensor
temperature
Accuracy error (°C)
max
Accuracy error (°C)
typ
Tempco (°C/°C)
2252 Ω
–40 °C
0.001
0.0007
0.001
0 °C
0.021
0.008
0.001
50 °C
0.263
0.130
0.001
120 °C
3.473
1.750
0.001
5000 Ω
–35 °C
0.001
0.0006
0.001
0 °C
0.009
0.004
0.001
50 °C
0.115
0.049
0.001
120 °C
1.535
0.658
0.001
10000 Ω
–25 °C
0.001
0.0005
0.001
0 °C
0.005
0.002
0.001
50 °C
0.060
0.028
0.001
120 °C
0.771
0.328
0.001
30000 Ω
–10 °C
0.001
0.0005
0.001
0 °C
0.002
0.001
0.001
50 °C
0.019
0.009
0.001
120 °C
0.267
0.128
0.001
Note 10:
Error shown does not include errors of the sensor itself. The sensor linearization is performed
using a Steinhart-Hart linearization algorithm. The accuracy and tempco specifications
include
the
accuracy of the Callendar-Van Dusen linearization algorithm. These specifications are for one year
while operation of the OM-WEB-TEMP is between 15 °C and 35 °C. The specification does not
include lead resistance errors for 2-wire thermistor connections. Contact your sensor supplier for
details on the actual sensor error limitations. Total thermistor resistance on any given channel pair
must not exceed 180 kΩ. Typical resistance values at various temperatures for supported thermistors
are shown in Table 8.
Table 8. Typical thermistor resistance specifications
Temp
2252 Ω
thermistor
3000 Ω
thermistor
5 kΩ
thermistor
10
kΩ
thermistor
30 kΩ
thermistor
–40 °C
76 kΩ
101 kΩ
168 kΩ
240 kΩ (Note 11)
885 kΩ (Note 11)
–35 °C
55 kΩ
73 kΩ
121 kΩ
179 kΩ
649 kΩ (Note 11)
–30 °C
40 kΩ
53 kΩ
88 kΩ
135 kΩ
481 kΩ (Note 11)
–25 °C
29 kΩ
39 kΩ
65 kΩ
103 kΩ
360 kΩ (Note 11)
–20 °C
22 kΩ
29 kΩ
49 kΩ
79 kΩ
271 kΩ (Note 11)
–15 °C
16 kΩ
22 kΩ
36 kΩ
61 kΩ
206 kΩ (Note 11)
–10 °C
12 kΩ
17 kΩ
28 kΩ
48 kΩ
158 kΩ
–5 °C
9.5 kΩ
13 kΩ
21 kΩ
37 kΩ
122 kΩ
0 °C
7.4 kΩ
9.8 kΩ
16 kΩ
29 kΩ
95 kΩ
Note 11:
Resistance values greater than 180 kΩ cannot be measured by the OM-WEB-TEMP in the
thermistor mode. The 180 kΩ resistance limit includes the total resistance across the current excitation
(±Ix) pins, which is the sum of the thermistor resistance and the lead resistances.
Note 12:
For accurate three wire compensation, the individual lead resistances connected to the ±Ix pins
must be of equal ohmic value. To ensure this, use connection leads of equal lengths.