C H A P T E R C
The LDT-5525 Temperature Controller uses v to determine the nominal temperature, Tn, by the formula:
Tn = ( v / ( 10mV / 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:
Td = C1 + ( C2 * Tn )
-where C1 and C2 are the constants stored by the user in the LDT-5525 Temperature Controller for the LM335.
When the LDT-5525 is shipped from the factory, the LM335 measurement system is calibrated, but the sensor (C1 and C2) is not. Nominally, C1 = 0, and C2 = 1. In that case, the temperature accuracy is typically +1oC over the rated operating range. With C1 and C2 calibrated also, the temperature accuracy is typically +0.3 oC over the rated operating range. The temperature accuracy may be improved over a narrow temperature range by a two-point calibration of C1 and C2. However, the LM335 is not perfectly linear, and even with C1 accurately known (and C2 uncalibrated) there is a non-linear absolute temperature error associated with the device. This non-linearity caused error is typically +0.3 oC, with the error associated with C1 assumed to be zero.
If a maximum absolute error of +1oC is tolerable, no calibration of C1 or C2 is required, just set C1 = 0, C2 = 1. If a maximum absolute error of +0.5 oC is tolerable, the one point calibration of C1 may be used (see page C-5). If a greater accuracy is desired, the two point method of determining C1 and C2 should used (see page C-6). Note however, the absolute error associated with the constant C2 may vary over different temperature ranges.
