Time Delay Unit (TD)
A solid-state time delay unit is used where machines do not come to an immediate stop. The insertion of one key will enable a time delayed run-down and the second ‘release for access’ key will remain captive until the desired condition of the machine or process has been achieved.
As part of an interlocked system, the time delay is used to control keys giving access to enclosed areas or machines where hazards may be present, until a safe condition has been achieved.
The time delay cannot start until the machine power has been shut off (1); the key from shut of is inserted into the time delay (2) to initiate the timer (3). When the timer is complete (4) the green button can be pressed to release the access key (5) and operate the interlock at the access point (6).
Combining the Time Delay with the Isolation Switch (TS)
The time delay is initiated by turning the integrated isolation switch. This simultaneously shuts off machine power. The gate access key is held captive in the unit until the desired condition of the machine or process has been achieved.
Voltage Sensing Unit (VS)
The VS unit measures the regenerative voltage produced by a motor and prevents removal of a gate access key until the machine has come to a rest.
The Voltage Sensing is a combination of an independently certified back-EMF unit, a solenoid controlled lock and a safety relay. It is typically used to ensure a trapped key sequence can only begin when the machine has come to a rest – where there is a ‘run down period’ such as mixers, motors, or high inertia roller systems.
Once the key is released, the machine cannot be restarted until the gate key has been returned.
Two illuminated push buttons are provided to give operator feedback as well as machine control. The blue pushbutton indicates the machine has come to rest. When the blue button is illuminated, it can be pressed to energise an internal solenoid and release the key.
The green push button illuminates when the safety circuits are in an open state. When the key is turned, the green will be illuminated. Pressing the green button whilst the key is inserted allows the safety circuits to be reset and allow machine restart.
The Voltage sensing unit monitors supply lines to the moto and is designed to detect open circuits or shorts on each input line. Where multiple access points are needed, the released key can be taken to an intermediate transfer system.
Time Delay and Voltage Sensing – Common Configurations
Key Initiated Time Delay in Stainless Steel enclosure, 24V Power to Unlock, with up to 5 minute timer (300s)
Switch Initiated Time Delay in Stainless Steel enclosure, 24V Power to Unlock, with up to 5 minute timer (300s)
Input Initiated Time Delay in Stainless Steel enclosure, 24V Power to Unlock, with up to 10 minute timer (600s)
Voltage Sensing Unit in Stainless Steel enclosure, 110V Power to Unlock, with up to 5 minute timer (300s)