32
CURRENTS
which are derived from the Hi Volts calibration value require an
additional span calibration to correct for the external resistor
(Customer supplied) – each channel
FREQ and SPEED
requires only a time base calibration shared for both channels
In general, to calibrate an analog input, first set the specific channel to an input type in the
ADVANCED SETUP MENU - CHANNEL SETUP - INPUT TYPE (see Section 4.1). Once
an input type has been chosen, select CALIBRATION (see Section 4.1). Do not change
the units from the default values set when that range is selected (i.e. leave volts as volts
and current as current).
Apply a "zero" value to the input and using the up (
▲
) and down (
▼
) arrow buttons adjust
the OFFSET until the onscreen indications shows zero.
Apply a "high" value to the same input and using the up (
▲
) and down (
▼
) arrow buttons
adjust the SPAN until the onscreen indication agrees with the input (Note – use an input
value slightly less than the full scale value to prevent an overrange indication).
Repeat for all input types and channels to be used, if not all of them.
5.1.2 EXAMPLES
Volts:
Should be done for the Lo Volts - 250mV, 1.25V, 2.50V ranges, and Hi Volts -
5.00V, 12.5V, 25.0V ranges using the 250mV and 5.00 volt ranges respectively. For each
channel individually, set the input for 250mV and go to Calibration. Short the input and
adjust the OFFSET until 0 is indicated. Then apply a near full scale input (so as to not
over range the input, say 240 mV on the 250 mV range) and adjust the SPAN.
Thermocouples:
(preferred method) First calibrate lo VOLTS range (250mV) for the
same channel as described above. Then switch to Thermocouple range. Select
NOMINAL to copy the volts calibration to thermocouple range. The recorder is now
calibrated for ideal sensors. Refine the calibration by either shorting the input (you need
to know the ambient temperature) or attaching a thermocouple sensor or calibrator of the
correct type for the selected range, and then if necessary, adjust the OFFSET until the
correct temperature is displayed – this corrects the ambient temperature sensor. If there's
a known "high" temperature source handy use that to fine tune the SPAN value.
Currents:
(preferred method) First calibrate Hi VOLTS range (5.00V) for the same
channel as described above. Then switch to any CURRENT range. Select NOMINAL to
copy the volts calibration to the current range. The recorder is now calibrated for ideal
resistor (250 ohm). Refine calibration for resistor and sensor current tolerances by
attaching a 250 ohm +0.1% resistor and input sensor matching the selected range. Apply
low value inputs to adjust the OFFSET value, and high value inputs to adjust the SPAN
value.
RTDs:
(preferred method) First calibrate lo VOLTS range (250mV) for the same channel
as described above. Then switch to RTD range. Select NOMINAL to copy the volts
calibration to RTD range. The recorder is now calibrated for ideal sensors and internal
current source. Refine the calibration by applying an accurately known resistance for a
given temperature (you may need resistance to RTD tables). Adjust the SPAN until the
correct temperature is displayed – this corrects for the internal current source.
Frequency
(RPM or Hz): Apply a calibrated frequency input near the high end of the
selected input range of either channel. Adjust SPAN until the indicated value is correct.
There is no applicable OFFSET adjustment to be made.
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