EARTH LEAKAGE MONITOR (679 series) CIRCUIT FUNCTION & SETTING INFORMATION.
DATA SHEET AVAILABLE THROUGH THIS LINK.
Operating Principal. Use in accordance with supplied product documentation.
The 679 Earth Leakage Monitor is a dc device designed to measure the output from power supplies and battery & battery charger installations and de-energises a relay if either pole is earthed either partially or completely.
Resistors CR1 and CR2, fitted to the earth leakage monitor pcb are connected across the DC supply rails derived from the battery connections made on terminals 2 (-) and 10 (+). The earth connection is made at the junction of CR1 and CR2.
Normally at 50% of the total supply voltage, the CR1-CR2 junction potential swings positive if an earth fault develops from positive to earth and negative if a fault develops from negative to earth.
Connected to the gate of T1 through a resistor is the CR1-CR2 junction. The source of T1 is normally at 47% of the total supply voltage and the resistors CR4 and CR5 provide a low voltage signal into pin 6 (inverting input) and pin 3 (non-inverting input) of the op amp IC1. Reference voltages are derived from CR6 and VR1 for pin 2 (inverting input) and CR7 and VR2 for pin 5 (non-inverting input).
A positive earth fault causes the potential on pin 6 (inverting input) to go positive with respect to pin 5 (non-inverting input) whilst a negative earth fault causes the potential on pin 3 (non-inverting input) to go negative with respect to pin 2 (inverting input).
Both positive and negative earth faults cause one of the op amp outputs (pin 7 for positive faults, pin 1 for negative) to switch from a positive potential to zero volts. This causes TR1 to switch off and the relay to de-energise.
The components C2, VR3 and D6 provide a delay from fault detection to relay de-energisation. R14 and Z2 provide the supply for the electronics.
VR2 adjusts the positive earth fault detection level and VR1, the adjustment for the negative earth fault detection level.
SETTING THE EARTH LEAKAGE MONITOR
To set the Earth Leakage Monitor, a dc supply voltage must be connected to the alarm monitor supply pins 2 (-) and 10 (+). The applied supply voltage must be at the normal operating level of the unit.
The Earth Leakage Monitor is set using a resistor value the same as R1.
Wind the potentiometers VR1 and VR2 clockwise until the red PCB mounted LED's switches off and the green led switches on.
Connect the resistor to pin 5 and the positive supply on pin 10.
Wind the potentiometer VR2 anti-clockwise until led 2 illuminates. After a short delay the relay should de-energise. Disconnection of the resistor from the positive supply should cause the on board relay to energise, the red led to switch off and the green led 3 to switch on.
Connect the resistor to pin 5 and the negative supply on pin 2.
Wind the potentiometer VR1 anti-clockwise until led 1 switches on. After a short delay the relay should de-energise. Disconnection of the resistor from the negative supply should cause the on board relay to energise, the red led to switch off and the green led 3 to switch on.
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