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Chapter 5
not perfectly linear, and even with C1 accurately known there is a non-linear absolute
temperature error associated with the device. This non-linearity caused error is
typically ±0.3°C, with the error associated with C1 assumed to be zero.
If a maximum absolute error of ±0.3°C can be tolerated, 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 associated
with the constant C2 may vary over different temperature ranges.
5.4.4.2.4
Determining C1 and C2 for the AD590 and LM335
The nominal values of C1 and C2 are 0 and 1, respectively, for both types of devices.
These values should be used initially for determining C1 and C2 in the methods
described below.
The One Point method is easiest, but it ignores the non-linearity of the device. It is
most useful when a high degree of temperature accuracy is not required.
The Two Point method can achieve a high degree of accuracy over a narrower
operating temperature range, but requires two accurate temperature measurements.
5.4.4.2.4.1
One Point Calibration Method
The calibration described in this section is independent of the calibration procedure
described in sections 7.3.4 and 7.3.6. Those sections deal with the internal calibration
of the TEC module, while the following calibration procedure is for calibrating the
external AD590 or LM335 sensor. For the most accurate possible results, both
calibration procedures should be performed.
The accuracy of this procedure depends on the accuracy of the externally measured
temperature. It is used to determine the zero offset of the device, and it assumes that
the gain (slope) is known.
Temperature Controller Operation
1.
Allow the 6000 to warm up for at least one hour. Select the desired
sensor type in the setup menu.
2.
Set the C1 parameter to zero. Set the C2 parameter to 1.
3.
Place the sensor at an accurately known and stable temperature, T
Connect the sensor to the 6000 for normal Constant temperature
operation. Allow the 6000 to stabilize at the known temperature, T
and read the displayed temperature, T
4.
Determine the new value of C1 from the formula:
.
d
C1 = T
- T
a
d
.
a
a
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