Electrode Check - ABB MAG-X 3000 Series Instruction Manual

INSTRUCTION MANUAL 10DX3111A&G Sizes 14 - 24 Inches
6.3.1.2 Model 10DX3111G
Verify that the system power service has been de-energized. Measure the resistance between
terminals M1 & MR on the Primary connection board. The indicated resistance reading should be
within the ranges shown in TABLE 6-1. A reading significantly outside this range or a short circuit
between leads indicates defective coil(s). Next, disconnect the the field wiring to the M1 and MR
terminals. Measure the resistance from each of these primary terminals to the flowmeter body.
Resistance from either of these leads to the body should be greater than 5 MΩ. A low resistance
reading may indicate that moisture has entered the meter interior. If the measured resistance is
within specifications, reconnect the wires to the terminal block.
If readings in this section are not within specification, the Signal Converter may display a "U-ref too
low" error message.

6.3.2 Electrode Check

The electrode check is essentially a resistance measurement that can be made to establish that a
short (or high resistance leakage path) does not exist between one, or both, electrodes and the meter
body. Verify that the system power service has been de-energized.
To thoroughly test the electrodes of the flowmeters, the meters must be tested under both full and
empty pipe conditions. If this is not possible, it may still be helpful to perform one of the tests since
useful partial information may be gained from the results of either portion of the test.
6.3.2.1 Full Pipe Test
The wetted electrodes of all flowmeters manufactured in accordance with FM Div.1 or Div.2 require-
ments must have energy-limiting resistance placed in series with them. Depending on the model
being tested, the nominal resistance value is 100,000 ohms and will add to any resistance measured
between the wetted electrode and the fluid in contact with that electrode.
Electrode full pipe measurements should be made with the ohmmeter placed on its highest range. An
AC type ohmmeter (i. e. conductivity bridge) is preferred because DC voltage will tend to polarize the
electrode (but will nevertheless provide meaningful information). Connect the ohmmeter positive
lead first to electrode terminal "1" and then to electrode terminal "2" with the negative lead to terminal
"3" or the flowmeter body. The measured resistance should be 100,000 ohms plus the intrinsic
resistance between electrode and fluid (typically 50,000 additional ohms or less). If using a DC
ohmmeter, the resistance between the electrode and the fluid will tend to increase as the electrode
becomes polarized by a DC signal. This effect is normal. AC resistance readings will not vary once
established. Readings greater than 150,000 ohms may indicate a coated electrode. Infinite readings
indicate a broken connection in the electrode wiring path. Meters with infinite full pipe readings
should be returned to the factory for repair.
6-4
TABLE 6-1. METER COIL RESISTANCE
METER SIZE
mm inches
350 14
400 16
450 18
500 20
600 24
COIL RESISTANCE
(Nominal, ohms)
Series Resistance
21.2
19.2
18.6
18.6
19.0