Contactors and Relays
Control relay easy, Multi
Function Display MFD-Titan®
Hold-on Circuit
A combination of series and
parallel contacts are wired
to a hold-on circuit.
The hold-on (self-maintaining) function is achieved by the Q1 contact being connected in parallel to I1. When I1 is actuated and reopened, the current flows via contact Q1 until I2 is actuated.
Logic table
|
I1
|
|
I2
|
|
Contact Q1
|
|
Coil Q1
|
|
0
|
0
|
0
|
0
|
|||
|
1
|
0
|
0
|
0
|
|||
|
0
|
1
|
0
|
0
|
|||
|
1
|
1
|
0
|
1
|
|||
|
1
|
0
|
1
|
0
|
|||
|
0
|
1
|
1
|
1
|
|||
|
1
|
1
|
1
|
1
|
The hold-on (self-maintaining) circuit is used to switch machines on and off. The machine is switched on at the input terminals via normally open contact S1 and is switched off via normally closed contact S2.
S2 opens the connection to the control voltage in order to switch off the machine. This ensures that the machine can be switched off even in the event of a wire breaking. I2 is always closed when not actuated.
Alternatively a hold-on
circuit with wire break
monitoring can used with the
set and reset coil
functions.
When I1 is switched, coil Q1 latches. I2 inverts the normally closed signal from S2 and switches when S2 is actuated and the machine must be switched off or when there is a broken wire.
Keep to the order that each coil is wired in the easy circuit diagram: first wire the “S”-coil, and then the“R”-coil. When I2 is actuated, the machine will then be switched off even if I1 is switched on again.