Kaman digiVIT - Manual (Page 20)

www.kamansensors.com PART NO: 860525-001
Last Revised 9/16/2013
- 20 -
6.8 Temperature Compensation (Electronics and Sensor)
While the digiVIT optimizes the sensor output for inherent temperature stability it can be
improved further by temperature compensation. The temperature of the sensor is measured
and used to compensate the output based on equations in the digiVIT. Optionally the
Electronics can also be temperature compensated separately from the sensors and uses a built
in temperature sensor for the compensation. In either case the compensation method is the
same. These equations are set by collecting data at 4 temperature points:
D1T1 -- Displacement 1, Temperature 1
D1T2 -- Displacement 1, Temperature 2
D2T1 -- Displacement 2, Temperature 1
D2T2 -- Displacement 2, Temperature 2
The digiVIT assumes that D1 is the same physical position for both T1 and T2. It does not
assume that the temperature of D2T1 is the same as D1T1.
As with any calibration temperature compensation depends on good fixturing. To some degree
if the fixturing is moving in temperature (due to material coefficient of thermal expansion – CTE)
the same way it does in the application the digiVIT will tend to compensate for it. In many cases
the digiVIT can be temperature compensated in-situ.
It is best to choose points D1 and D2 at 10% and 90% of the range (D1 could be 90% and D2
could be 10% -- does not matter). If the expected usage is in a narrower range, better results
could be obtained in the important displacement band by calibrating over the narrower range.
1) Select 'Cal Setup -> Temp Cmp Sensor' from the front panel. The prompt will read
'GotoD1T1 relC 0’. At this point it expects to be at Displacement 1 Temperature 1 in a fixture. A
good method is to fixture it at 90% of displacement (approximately -- it does not matter
precisely) and the heat the sensor head (if cable is going to be in the hot environment it should
also be included). You will see the relC x indicator rise as temperature increases and fall as it
decreases. It works best to heat it up and then let it cool down just a bit before taking the first
data point so that transient effects are not included. Typically if the sensor is heated until the rel
C reads 10 or 12 or more that is sufficient. Let it cool down slightly to say 11 or even 9 and
press <enter>.
2) The prompt will read 'GotoD1T2 relC 8'. Let it cool down until it is close to where it started
though it is not necessary to let it cool down all the way. Then press the <enter> button.
3) The prompt will read 'GotoD2T1 relC 1'. Reposition the sensor in the fixturing to be at a
second displacement. Typically 10% of the range is good setting. Again it is best to heat it up,
let the transient go away and press the <enter> button at a rel C of 10 or 12. After the transient
has gone away, press the <enter> button.
4) The prompt will read 'GotoD2T2 relC 9'. After the temperature goes down to near 1 or 2
press the <enter> button and the temperature compensation is complete.