LOGO! realizes intelligent alternating start and stop between two compressors

In industrial production, it is sometimes necessary for two compressors that share a power supply line to be able to start and stop alternately. When one compressor fails, the other can start automatically. Moreover, these two compressors need to be able to operate separately in manual or automatic mode.

LOGO! Solution

In the design of this program, a selector switch is provided for each compressor to select manual or automatic mode.

For compressor 1, the manual setting is connected to I1 and the automatic setting is connected to I2. The manual setting of the second selector switch is connected to I3 and the automatic setting is connected to I4.

When one of the compressors starts, the main contactor is first activated for enabling and then after a delay of 2 seconds it is started via the floating contactor

For compressor 1, the contactor is connected to Q1 and the start is via Q3. For compressor 2, the contactor is connected to Q2 and the start is via Q4.

Two operating modes

Manual operation

Only one compressor can be operated. For compressor 1, the selector switch must be set to "manual" (connected to I1) and the selector switch of the second compressor must be set to 0.

If you want to operate compressor 2 in manual mode, the selector switch must be set to "manual" (connected to I3) and selector switch 1 must be set to 0.

Automatic mode

In automatic mode, the two compressors operate alternately. This requires setting both selector switches to "automatic" (connected to I2 and I4).

Practical application scenarios

During the day, from 7 am to 6 pm, compressor 1 will run if there is sufficient pressure. For this purpose, a pressure monitor is connected to I5.

If there is still sufficient pressure

In the period from 6 pm to 7 am, a switchover to compressor 2 will take place. However, before the switchover, the compressors must run for a certain period of time. For compressor 1, the preset running time is 50 seconds and for compressor 2 25 seconds.

If one of the compressors fails due to insufficient pressure

Switchover to the other compressor will be automatic. Even if there is sufficient pressure again, this compressor can only be switched off if both selector switches are set to 0. Automatic mode must then be reselected.

If a response from I5 is triggered due to insufficient pressure

This will be signaled at Q5 by a fault light. The fault can be acknowledged via I6.

If the pressure remains below the preset value for more than 2 minutes

A flashing light will appear at Q6. This alarm signal will continue until there is sufficient pressure again.