MESSTEC Power Converter GmbH
Operating Manual
TEC Controller
Document: 10100920OM
Revision: 1.1
Date: 10.10.2019
Page 26/71
5.6. Sensor Current
The current source for the temperature sensor is adjustable between 100 µA and
4 mA. Default setting is 1 mA.
Note: For almost all sensors, the default setting fits very well. It is therefore not
necessary to alter the sensor current. In seldom cases, especially with
specific sensors (see chapter Arbitrary Sensor) it may be necessary to alter
the sensor current to optimize the measurement results.
Supplementary detailed information:
The current through the temperature sensor is always the result of a reasonable compromise.
Conflicting requirements are:
Maximized sensor output signal hence optimized resolution
Minimized sensor power hence self-heating
Sensor signal processing has upper and lower limits
It is a common rule of thumb, to limit the load of the sensor to 1 mW. With this value self-
heating of the sensor device is acceptable low and the sensor output signal is high enough
for precision signal processing.
Sensor signal processing limits are:
U
MIN
: 0,08 V
U
MAX
: 2,30 V
Sensor voltages below U
MIN
are considered as short-circuit in the sensor circuit. Sensor
voltages above U
MAX
are considered as broken wire in the sensor circuit. A sensor error is
released in both cases.
For the sensor current we have:
𝐼
𝑆𝐸𝑁𝑆𝑂𝑅 𝑀𝐴𝑋
= √
𝑃
𝑆𝐸𝑁𝑆𝑂𝑅 𝑀𝐴𝑋
𝑅
𝑆𝐸𝑁𝑆𝑂𝑅
and
𝑈
𝑆𝐸𝑁𝑆𝑂𝑅
= 𝑅
𝑆𝐸𝑁𝑆𝑂𝑅
∗ 𝐼
𝑆𝐸𝑁𝑆𝑂𝑅
Example:
What is the current value for a Pt1000 sensor, when the power dissipation is supposed to be
1 mW?
𝐼
𝑆𝐸𝑁𝑆𝑂𝑅
= √
0,001 𝑊
1000 Ω
= 1 𝑚𝐴
𝑈
𝑆𝐸𝑁𝑆𝑂𝑅
= 1000 Ω ∗ 1 𝑚𝐴 = 1,0 𝑉
Result:
The proposed sensor current is 1 mA.
The sensor voltage is 1 V. This is very well between the two limits U
MAX
and U
MIN
.