SRS Labs CTC100, Руководство пользователя

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Introduction 6
CTC100 Programmable Temperature Controller
excitation is too large it will heat the sensor and cause higher than expected readings. Therefore,
e
Low power: minimizes sensor heating. This option is mainly for use with thermistors in
cryogenic applications. To compensate for the fact that heat conductivity decreases (and
thermistor resistance increases) as the temperature approaches absolute zero, the amount of
power that the sensor dissipates decreases as the measurement range is increased.
High power: minimizes noise. Power dissipation is kept roughly constant as the
measurement range is increased. This option is for use with RTDs or with any kind of sensor
at non-cryogenic temperatures.
Auto power: uses low power if the sensor type is set to thermistor or ROX, or high power
if the sensor type is set to RTD.
The CTC100 has 12 measurement ranges. Within any given range, it generates a constant
excitation current as shown in the table below. Note that the range has to be greater than the
sensor resistance, so if the sensor resistance is 10 k , for example, the range should be 30 k .
For diode sensors the range is always 2.5V and the excitation current is always 10 µA.
The graph below shows how the amount of power dissipated by the sensor depends on the range
and power settings. Sensor heating (degrees above the ambient temperature) is proportional to
power dissipation.
Left: the amount of current passed through the sensor by the CTC100;
right: the amount of power that the sensor dissipates due to that current
The table below shows some representative noise, electronic accuracy, and self-heating values for
free-standing sensors at room temperature. Note that the amount of self-heating can vary
dramatically depending on the thermal conductivity of whatever the sensor is attached to or
immersed in.