Wahl Digi-Stem DST600 Series User Manual page 11

DST600 Series USER MANUAL
To achieve this we will be using the programmable RO value in the
DST6xx Series TID, which is accessed using the DSTCAL program. The
R0 value (R0 stands for resistance at 0°C), is a variable in the equation
for converting resistance to temperature for platinum RTD's and is factory
set to match the specific value of the probe connected to the DST6xx.
Without going into great detail of the equation and its variables, the R0
variable essentially serves as an offset control, shifting the response
curve up or down the scale. Since the slope of the curve is controlled by
other variables that are not programmable, different meters may have
slightly different response to the same change in R0.
The process for performing this type of adjustment is as follows:
1) Measure the system error by putting the meter and probe into a stable
liquid bath monitored by an appropriate standard instrument (Reference
Device) and record. This should be measured at a temperature
representative of your process temperatures.
2) Determine the error and note if it is positive (TID > Ref. Dev.) or
negative (TID < Ref Dev.).
3) If error is negative, no action is needed.
4) If error is positive, R0 will need to be increased to lower the
temperature displayed. A good starting point is:
A + .03 ohm adjustment to R0, will drop the reading by about 0.2 to 0.3°F
A + .06 ohm adjustment to R0, will drop the reading by about 0.4 to 0.5°F
5) After adjustment, repeat step 1. If the results meet your requirements,
record this data on your calibration form and this will be your new
calibration record. Be certain to record your results and mark your
equipment in accordance with 21CFR part 113.100.
6) If the results still do not meet your requirements, then increase R0
slightly and repeat step 5.
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