The DTEC Ltd. GFIV1.2 ground fault monitoring board places a high impedance (~2M2 ohms) voltage source of +25.6 VDC, with respect to chassis ground, onto eight channels. It then measures the drop across sensing resistors. These (1M2 single phase 1M8 3 phase) sensing resistors are found either installed on the GFIV1.2 termination board or installed in an epoxy block close to the high voltage source. If a ground fault condition is developing this +25.6 vdc level decreases. If +25.6 VDC is measured with respect to chassis ground on the monitored channel there is no ground fault. As the this voltage drops, a corresponding decrease in the ground fault resistance level is sensed and an increasing analog output voltage for that channel is produced. If the ground fault level becomes less than an equivalent of 500K ohms to ground the digital alarm is raised on the board.
There are 5 sections to the circuit board:
Note:lsb : Least Significant Bit
msb : Most Significant Bit
0 : Logic Ground
1 : Logic +15 vdc
The ground fault board is set up at the
factory to measure ground faults ranging from
No foreign wiring (system interconnections to sense lines) should be connected to the board only the essential wiring.
Connections for the board
Edge Term board
C2 39 Chassis Ground
C4 38 Logic Ground
C10 1 Logic +12 vdc
C12 2 Bit Select 1 (lsb)
C14 3 Bit Select 2
A14 4 Bit Select 3 (msb)
C16 5 Digital Output Alarm For Channel 1
C18 6 Digital Output Alarm For Channel 2
C20 7 Digital Output Alarm For Channel 3
C22 8 Digital Output Alarm For Channel 4
A16 9 Digital Output Alarm For Channel 5
A18 10 Digital Output Alarm For Channel 6
A20 11 Digital Output Alarm For Channel 7
A22 12 Digital Output Alarm For Channel 8
C26 36 Channel 1 Input Sense Lines
C28 34 Channel 2 Input Sense Lines
C30 32 Channel 3 Input Sense Lines
C32 30 Channel 4 Input Sense Lines
A26 28 Channel 5 Input Sense Lines
A28 26 Channel 6 Input Sense Lines
A30 24 Channel 7 Input Sense Lines
A32 22 Channel 8 Input Sense Lines
Test points used on the board
Input logic voltage level point and ground point found in the rear left corner.
Chassis ground point found near LED 8
TP1 found near power LED9 and C18
TP3 found near C19 and P10
Tune Pot 11 (P11) so the voltage at Test Point 1 (TP1) is +6.00 vdc with respect to chassis ground. This calibrates the digital output trip level to activate at ~500K ohms. Tune Pots 1 through 8 (P1 to P8) so the voltage at the junction of the diode and capacitor is +10.00 vdc with respect to chassis ground. For example to set up channel 1: - place the + ve probe of multi-meter on the junction of D1 (diode 1) and C1 (capacitor 1) and the - ve on the chassis ground. - tune P1 until the multi-meter reads +10.00 vdc. E.g. To setup channel 4: Remove U8. U8 cannot output a negative voltage which is required on setup of the board. U8 will be replaced later. Place a full ground fault (two 1M2 resistors in series from chassis ground and the input) on channel #1 (C26). If using the terminal board connect chassis ground to both terminal #36 and terminal #35. Tune Pot 10 so that the analog output at pin 3 of U8 is 5.00 VDC. Remove the ground fault on C26 and tune Pot 9 so that the voltage out is -0.83VDC. Replace the ground fault on C26 and re-tune Pot 10 continuing to go between the no ground fault condition and ground fault condition tuning Pot 9 and Pot 10 respectively.
** Note **
If you are using the DTEC GFM-3 termination board you must tie the 2 input sense together ( 35,36 - 33,34 etc.) so the sense resistors are parallel. If they are already connected to a power supply or a transformer they dont need to be tied together but you should be wary of trying to setup the board in circuit as ground faults even of a small magnitude will throw off the setup values.
Jumper 1 JP1 - This selects the digital output from either active high or active low.
Jumper installed is active low. Jumper removed is active high. Jumper 3 JP3 - +5 vdc or +15 vdc - This is a hard wire jumper found in front of P11.