Interlock: safety cirtcuit -

17 Sep 2022, 19:50
Marián Hubinský
Technologies
1711 views
Tags: Power supply, interlock, safety, inhibit

A frequently requested function on electrical equipment is to quickly turn off the output of the power supply in case of unexpected event, such as opening of a door by an operator or an emergency stop of the production line. In such cases, the safety circuit is initialized by opening the loop (OK status means a closed circuit). Power supplies manufactured by Delta Elektronika label this feature as INTERLOCK (Inhibit) and is factory-installed on SM series power supplies. Each power supply is shipped with factory installed connector and a jumper. If the Interlock circuit is opened (Fault status), the RSD indicator lights up and/or the Interlock symbol () appears on the display.

While in rest state, voltage of ±5V is present on the Interlock input socket and output from the power supply is off and locked. To unlock the power supply output, the Interlock circuit need to be closed by a jumper, switching contact or optocoupler (optron).

Due to different design of power supplies, the Interlock circuit is always at a different potential.

The SM800, SM1500 a SM6000 series power supplies share the potential with negative pole of the power supply's power output, while the SM3300 and SM15K series share the Interlock potential with the protective earth PE (Metallic frame of the power supply). In addition, it is possible to insert an extension card - INT MOD CON, which contains another Interlock circuit which has floating potential. The Interlock input is usually labeled as CON A or CON F.

Every power supply also powers it's own Interlock circuit, hence it is not possible to connect different Interlock circuits in parallel nor series. In cases where there are multiple power supplies in a single rack or switchboard and we need to switch off all the outputs, every single power supply has to have it's own galvanically insulated switch. In most cases, this can be done with the help of a relay.

The SM3300 and SM15k solve this problem easily - inserting the INT MOD CON extension card which apart from having a floating potential also has ENABLE input, which reacts to 24V signals. This allows you to connect multiple power supplies in parallel to one 24V signal as the ENABLE input is passive and all of the other individual inputs will not be affected.