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5300 Series TECSource User’s Manual · Page 27
Working With AD590s and LM335s
Unlike thermistors and RTDs, an AD590 or LM335 is considered an “IC” sensor
because it has an active transistor element that responds to changes in
temperature by producing a current (AD590) or voltage (LM335).
Also unlike thermistors and RTDs, these IC sensors produce a linear response,
making conversion to temperature a very straightforward calculation.
AD590 sensors produce 1 μ A/K, so that 0°C (which is equal to 273.15K) would
produce 273.15 μ A.
Similarly, LM335 sensors produce 10mV/K, so that 0°C would produce 2.7315V.
For both sensors, because the response is linear, the sensor coefficients default
to a slope of 1 and an offset of zero, but can be adjusted to achieve higher
accuracy.
The temperature correction formula for the AD590 or LM335 is:
T = MT
C
+ B
Where T
C
is the temperature (in °C) calculated using the standard conversion
value of 1°C/ μ A or 0.1°C/mV, as appropriate, and adjusted from Kelvin to
Celsius.
Controlling the Temperature Rate of Change
Some applications require that temperature is changed at a specific rate to
prevent damage that might otherwise come from rapid changes in device
temperature. Using the
T Rate setting in the menu, it is possible to control the
temperature ramp rate of the controller, limiting the rate of change to specific
degrees Celsius per minute.
Because the temperature rate function relies on the instrument tracking a
gradually changing set point, a proper gain setting (or PID values) are important
to achieve a smooth and continuous temperature transition.
To disable the temperature rate function, simply set T Rate to 0.0°C/min.