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6.5 Calibration
The pressure channels in the PLC can be
periodically calibrated for highest measurement
accuracy. The temperature and optional frequency
channels do not require calibration.
Because calibration standards with known values
are the basis for accurate test results, never guess
at the value of the standard. As a rule, the source used to calibrate a sensor should be 10 times more
accurate than the sensor being calibrated. For example, if a sensor has an accuracy of ±1%, the standard
used to calibrate it should have an accuracy of ±0.1%.
The pressure transducers used in the flowbench have an accuracy of better than ±0.5%. Therefore, unless
you have access to a very high-quality pressure calibrator, the accuracy of your flowbench after calibrating
it will be no better than the standard you use.
The flowbench was calibrated at the factory. The saved calibration values can be read by reading the
proper registers. Refer to "4.2.1 Modbus List" on page 11 for a complete list of registers.
6.5.1 Calibrating Sensors
Pressure Calibration
Calibrate the Test and Flow pressure channels
using an accurate, calibrated vacuum pressure
source that reads in inches of water (inH
2
O).
Verify Calibration
1. Make sure there is no pressure source
connected to the pressure transducer
being check and the reading register
(
40047-48 TestPressureFloat
or
40049-50
FlowPressureFloat
) to verify
zero (0) pressure.
2. Remove the
Low
port vinyl hose from the
pressure transducer being checked and
connect a calibrated vacuum pressure source
to the
Low
port and then apply a pressure of 25 inH
2
O.
3. Verify pressure transducer reading by reading the appropriate register (
40008 FlowPressure
or
40009
TestPressure
). If read matches the calibrated pressure source within
(+/-) 0.25% the current calibration
has been verified. If calibration adjustments are required, follow calibration steps on the following page.
DO NOT try to recalibrate the sensors unless you
have an accurate vacuum pressure source or
barometric pressure data.
!
WARNING
Figure 6.10: Pressure Transducers
Test Pressure
Transducer
0-100 inches of
water (inH2O)
Flow Pressure
Transducer
0-50 inches of
water (inH2O)
Low
High
6.0 Maintenance
