The name ‘volt free contact’ may suggest that volt free
contacts operate without any voltage, but this is not the case.
Volt free contacts are mechanical switches that have no
electrical connection to any other part of the equipment. This makes the circuit
intrinsically safe. They are sometimes referred to as the secondary sets of
contacts of a relay circuit, which does not make or break the primary circuit
being controlled by the relay. This allows volt free contacts to provide
complete isolation between devices in the circuit.
Volt free contacts operate like an ordinary switch. When
required, the switch closes, allowing current to flow through to trigger other
systems to perform an action, such as lighting a lamp or sounding an alarm.
Volt free contacts are also known as ‘dry contacts’ or
‘potential-free contacts’.
Standard Volt Free Connection sets supplied by Applied
Thermal Control allow for the monitoring of alarms, allowing flow, temperature,
level and all-OK VFCs to be communicated across 5 wires of D-sub 9pin, at 24V
DC. In cases of high flow, temperature within a detectable range, or high
levels, the circuit will close, causing a signal to be sent.
Other
alarms can be transmitted via VFC when specified and available.