Figure 36 Ad590 Nonlinearity - Newport 6100 User Manual

124 Principles of Operation
where i is the nominal current produced by the AD590, and K is in Kelvin.
The 6100uses i to determine the nominal temperature, T , by the formula:
n
= (i /(1 A / K) ) - 273.15
T
n
is in C.
where T
n
The displayed temperature, T = C1 + (C2 * T ), is then computed, where C1
d n
and C2 are the constants stored in the 6100for the AD590. The AD590
grades of tolerance vary, but typically, without adjusting C1 and C2, the
temperature accuracy is 1C over its rated operating range. However, the
AD590 is not perfectly linear, and even with C1 accurately known there is a
non-linear absolute temperature error associated with the device. This non-
linearity is shown in Figure 36, reprinted from Analog Devices
specifications, where the error associated with C1 is assumed to be zero.
Figure 36 AD590 Nonlinearity
If a maximum absolute error of 0.8C is tolerable, the one point calibration of
C1 should be used. If a greater accuracy is desired, the two point method of
determining C1 and C2 should be used. Note however, the absolute error
curve is non-linear, therefore the constant C2 will vary for different
measurement points.
6.3.2.3 LM335 Sensor
The LM335 is a linear thermal sensor that acts as a voltage source. It
produces a voltage, v, which is directly proportional to absolute temperature,