ABB K-MAG 10D1476 Instruction Manual page 50

10D1476 K-MAG MAGNETIC FLOWMETER INSTRUCTION MANUAL
6.3.3 Flowmeter Board
The Flowmeter board is located in the base of the electronics housing as shown in Figure 6-1. This
pc board includes the constant meter factor/size network. The constant meter factor/size network is
used to standardize the particular flowmeter; i.e., provide a meter CAL FACTOR that will be the same
for all meters of the same size.
The constant meter factor/size network is factory set by precise calibration prior to shipment. Further,
this calibration procedure (used to establish the exact setting for the particular constant meter
factor/size network) also compensates for variations resulting from manufacturing tolerances. The
value of constant meter factor/size network on each Flowmeter board is unique and may be applica-
ble only for the particular flowmeter for which it was supplied.
Replacement of the Flowmeter board in the field is not recommended. Should board replacement
become necessary, the following steps must be followed:
1. De-energize the Signal Converter power source (this will remove power from the primary).
2. Before removing the board, it will be necessary to unsolder the 8 leads from the RFI capacitors
(see Figure 5-1), plus the 3 leads from the meter electrodes, and the four wires from the magnet coils.
Use care to identify all leads to ensure proper reconnection.
3. When primary connections to the board have been disconnected, remove the 3 # 4-40 board
mounting screws. The board can now be removed from the meter base.
The following procedure is required to maintain the accuracy of the meter Cal Factor.
4. Potentiometer R14 and resistor R15 must be carefully removed from the old circuit assembly (note
the orientation of potentiometer R14). If they are in usable condition, place them into the new
assembly (observe R14 orientation). If they cannot be used, then measure and record the resistance
of the following components to an accuracy of 0.1%:
R15, R14 pin 1-2, R14 pin 3-2 ("2" is the wiper)
Calculate the following:
K = (R15 + R14 pin 1-2) / (R15 + R14 pin 1-2 + R14 pin 3-2)
5. Remove R14 and R15 from the replacement assembly. Measure R15 and adjust R14 to obtain the
same "K" as calculated in step 4. Place R14 and R15 back into the circuit board, noting the proper
orientation of R14.
6. Note which positions of shunt S1 were opened in the old CMF board. Open the identical shunt
positions of S1 in the replacement board.
7. Replace the CMF board in the meter base and restore intraconnection wiring.
8. A zero flow, full pipe condition in the primary must now be established and the system powered.
An oscilloscope must be connected to TP5 (TP1 com.) of a CD-1 Converter or TP103 (TP101 com.)
of the XM Converter. CD-1 Converters must be set to a 1 ft/sec range and placed into self-test
(elevated). R3 of the CMF assembly must be adjusted for a peak to peak waveform value of less than
2 volts (CD-1) or 0.2 volts (XM).
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