Lightwave Communications LDT-5525 manual AD590 AND LM335 SENSOR CALIBRATION, AD590 Sensor

A P P E N D I X C

AD590 AND LM335 SENSOR CALIBRATION

The LDT-5525 Temperature Controller uses two constants (C1 and C2) for calibrating linear thermal sensing devices, such as the AD590, and the LM335. C1 is used as the linear or zero offset value, and C2 is used as the slope or gain adjustment. Therefore, C1 should be set to a nominal value of 0, and C2 should be set to a nominal value of 1, when the SENSOR SELECT switch is in the AD590, or LM335 positions.

In order to calibrate a linear sensor device, the sensor must be operated at an accurately known, stable temperature. For example, the sensor may be calibrated at 0oC if the sensor is placed in ice water until its temperature is stable. A highly accurate temperature probe, thermometer, environmental chamber, etc., may also be used to determine the known temperature for calibration. This appendix contains one and two point calibration methods for linear sensor devices. These methods will work for either type of device.

AD590 Sensor

The AD590 is a linear thermal sensor which acts as a constant current source. It produces a current, i, which is directly proportional to absolute temperature, over its useful range (-50oC to +150oC). This nominal value can be expressed as:

i = 1∝A / K

- where i is the nominal current produced by the AD590, and K is in Kelvin.

The LDT-5525 Temperature Controller uses i to determine the nominal temperature, Tn, by the formula:

Tn = ( i / ( 1∝A / K ) ) - 273.15 - where Tn is in oC.

The temperature, Td, which is displayed by the LDT-5525 Temperature Controller is first calibrated as follows:

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