Features
• Consistent accuracy
• Reliability
• Low burden
• Reduced maintenance
• Immunity to transients and surges;
withstands 5 kv impulse voltage test
• Relays with heavy-duty magnetic
blow-out contacts also available

Description
A stabilised voltage is applied to a
resistance/capacitance circuit. The
potential developed across the capacitor
is applied to a transistor switching circuit
which, in turn, operates an attracted
armature relay when the potential
reaches the trigger level.
The time delay is varied by altering
the resistance value in the resistance/
capacitance circuit by a potentiometer
calibrated in seconds. A circuit is
incorporated to protect the transistors
from damage due to high peak transients
in the supply voltage. A diode is also fitted
in the circuitry to take care of inadvertent
connection of supply with reversed
polarity
Type VTT 11 units have a delayed pickup,
i.e., timing is started by closing an
initiating contact and the output relay is
energised at the end of the set time. The
unit resets when the initiating contact is
reopened.
Type VTT 12 units have a delayed dropoff,
i.e., the output relay is normally
energised. Timing is started by opening
an initiating contact and the output
relay is deenergised at the end of the set
time. The unit resets when the initiating
contact is reclosed.