Appendix A: Ad590 And Lm335 Sensor Calibration; Ad590 Sensor - Newport LDC-3706 Series User Manual

Appendix A:
AD590 and LM335 Sensor Calibration
The LDC-3706 Laser Controllers use two constants (slope and offset) for calibrating linear IC
thermal sensing devices, such as the AD590, and the LM335. Offset is used as the linear or
zero offset value, and the slope is used as the slope or gain adjustment. Therefore, when
accuracy is not critical, offset should be set to a nominal value of 0, and slope should be set to a
nominal value of 1 when the selected sensor is an IC-I or set to a nominal value of 10 when the
selected sensor is an IC-V.
In order to calibrate an IC sensor device, the sensor must be operated at an accurately known,
stable temperature. For example, the sensor may be calibrated at 0 °C 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 IC sensor devices.
These methods will work for either type of device.

AD590 Sensor

The AD590 is a linear IC thermal sensor which acts as a constant current regulator. It produces
a current, I, which is directly proportional to absolute temperature, over its useful range
(-50 °C to +150 °C). This nominal value can be expressed as:
= 1
Where I is the nominal current produced by the AD590, and K is the temperature in Kelvin.
The LDC-3706 uses current to determine the nominal temperature, T , by the formula:
n
= − 273.15
1
Where T is in °C.
n
The temperature, T , which is displayed by the LDC-3706, is first calibrated as follows:
d
= + ( ∗ )
Where offset and slope are the constants stored by the user in the LDC-3706 for the AD590.
The AD590 measurement is calibrated, at the factory, with C = 1 and C = 0 (nominal values).
2 1
The AD590 grades of tolerance vary, but typically this means that without adjusting C or C , the
1 2
temperature accuracy is ±1°C over its rated operating range. If C and C are also calibrated,
1 2
the temperature accuracy is ±0.2°C over its rated operating range. However, the AD590 is not
perfectly linear, and even with C accurately known there is a non-linear absolute temperature
1
error associated with the device. This non-linearity is shown in Figure A.1, reprinted from Analog
Devices specifications, where the error associated with C is assumed to be zero.
1
December 2019 107 LDC-3706 Series Laser Controller