Siemens Milltronics MFA 4p Operating Instructions Manual page 28

Troubleshooting
6.1 Troubleshooting
Notes:
● Voltage levels are DC, nominal values, and may appear to be pulsing, coincidental with
LED 1.
● If diagnosis does not solve the malfunction, the probe, pre-amp or MFA 4p may be
defective.
● If no spare circuit boards or probes are available for interchanging, the MFA 4p may be
tested as follows in order to determine which section is defective:
– To find out if the MFA 4p is defective:
– To find out if the RMA is defective:
– To find out if the probe is defective (non-IMA type only; i.e. MSP-3 and MSP-9):
26
i. Disconnect the pre-amp.
ii. Set ppm switch SW2 to X 1 position and turn potentiometer to 15.
iii. Connect one Iead of a 530 ohm, 1 watt resistor to terminal 7 and then momentarily
contact terminal 8 at a rate of once per second. If the MFA 4p is functional, the relays
will energize after two puIses and de-energize approximately 8 seconds after last
pulse.
i. Disconnect pre-amp from the MFA 4p. Attach probe across terminals TB1 1/2 and a
24 V DC (floating) power supply across terminals TB2 3/2, according to the MSP-3 or
MSP-9 Probe with RMA (remote mounted amplifier) (Page 14) connection diagram.
ii. Run equipment to be monitored at normal operating speed or pass a ferrous object
in front of and as close to probe as possible at a continuous rate.
iii. With an oscilloscope, look for approximately 6 V peak to peak pulses or alternating
hi/lo levels across ground and link 3. Or with an amp meter connected in series
between the RMA and the 24 V DC power supply, Iook for hi/lo levels of approximately
12 mA/40 mA alternating at the rate of the passing ferrous objects.
i. Disconnect probe from pre-amp.
ii. Connect an ohm meter across the black and white leads.
iii. Nominal probe impedances are as follows:
MSP-3 and MSP-9
If impedance deviates substantially from these values, an open or short circuit
condition is indicated.
750 ohms
Operating Instructions, 08/2017, A5E33988839_AB
Milltronics MFA 4p