Scope
This Guideline provides a method to check the Analogue to Digital
Conversion (ADC) input channel(s) on each flow computer. A controlled
analogue signal (4 – 20 mA) is injected into a computer analogue input at the
back of the panel and the digital conversion is confirmed by reading the
computer display and comparing it with the expected value.
Frequency As needed
ANALOG TO DIGITAL CONVERSION CHANNELS | FLOW COMPUTER
PREPARATIONS:
Ensure that the meter stream is off-line and out of service.
Give a brief description of the test in the Metering Log Book.
Record the results of the test on the Analogue to Digital Conversion
Test Sheet., attached.
Verify that the certificates for the test equipment are valid. Check that
the test equipment serial numbers and certification dates are
accurately recorded on the test sheet and correspond with the test
equipment used. Ensure the flow computer tag and serial numbers
are recorded on the test sheet.
CALIBRATION EQUIPMENT:
A) DC Current Source
B) Digital Multimeter
PROCEDURE:
The flow computer ADC shall be checked using the following
procedure: –
a) Confirm that the flow computer external and internal power
supply voltages are within acceptable tolerance. If necessary,
adjust internal volt rails according to flow computer instruction
manual.
b) Select and disconnect a transmitter field input at the back of the
panel.
c) Connect the DC current source in series with the transmitter field
input.
d) Connect the digital multi meter in series with the transmitter
and monitor the input.
e) Check the ADC by inputting current at the following nominal
points of span both rising and falling, 0, 25, 50, 75 and 100%.
f) Note the flow computer displayed value for five points of span
both rising and falling.
h) Complete the analogue to digital conversion test sheet. If the
input and displayed values are within tolerance the test is
complete.
i)
If the input and displayed values are out of tolerance the ADC
requires adjustment. This may be a potentiometer or
configuration adjustment – consult the flow computer instruction
manual. It may be necessary to return the unit to the
manufacturer and replace it with a spare.
i) Once the input and displayed values is within tolerance
complete the test sheet and ensure it is marked with
appropriate comments.
j) Enter details of all tests in the Metering Log Book. Record if
the flow computer has been replaced and the serial number of
the replacement unit.
ANALOG TO DIGITAL CONVERSION INPUT TEST SHEET – TS 001
