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Omega Model CYD201/202 User’s Manual
2-10 Installation
Sensor Mounting (Continued)
CAUTION:
Omega will not warranty replace any device damaged by user-
designed clamps or solder mounting.
For semi-permanent mountings, use Stycast epoxy instead of Apiezon
®
N
Grease.
NOTE:
Do not apply Stycast epoxy over the CY7-SD package--sensor
stress may shift the readings. In all cases, periodically inspect the sensor
mounting to verify good thermal contact to the mounting surface is
maintained.
2.4.4
Current Source Dependence
This paragraph addresses the effects of current source accuracy on
temperature measurement accuracy. Although the Model CYD201 has an
accurate internal current source, it is important to understand the
relationship between current variation and measurement accuracy.
Diode sensors possess a non-linear forward current-voltage characteristic.
Consequently, the forward voltage variation with changing current for diodes
is smaller than for resistance temperature sensors, which have linear
current-voltage characteristics.
Below 30 K, the sensitivity (dV/dT) of Omega Engineering diode
temperature sensors increases by an order of magnitude over sensitivities
at higher temperatures. The slope (dV/dI) of the I-V curves stays relatively
constant. Both characteristics reduce even further the effect of any change
in forward bias current on temperature measurement accuracy. Refer to
Tables 2-1 and 2-2.
Table 2-1. Effect of Current Variation
on Diode Temperature Measurement Accuracy
T (K)
∆∆∆∆
I, µA* Acc. (%)*
Range (µA)*
Error (K)
300
0.5
0.05
0.005
5
0.5
0.05
9.5 to 10.5
9.95 to 10.05
9.995 to 10.005
1
0.1
0.01
150
1
0.1
0.01
0.005
10
1
0.1
0.05
9 to 11
9.9 to 10.1
9.99 to 10.01
9.995 to 10.005
1
0.1
0.01
0.005
50
3
0.3
0.03
0.005
30
3
0.3
0.05
7 to 13
9.7 to 10.3
9.97 to 10.03
9.995 to 10.005
1
0.1
0.01
0.005
* With current source (I
≈
10 µA).
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