• 1. Pulse signal type
• 2. Wiring
• 3. Electronic gear 
• 4. Changing direction

In this article, I will describe how to change the rotation direction of the Slave inverter during synchronisation to pulses from the Master inverter.

A general description of Master-Slave synchronisation of FR-A800 inverters with wiring diagrams and parametrisation procedure is in the attachment – “Master-Slave vector control with FR-A8AL”

In general, in the configuration where phases of the encoder from the Master inverter are connected to input terminals of the A8AL card in the Slave inverter, during synchronisation ( Pr.419=”1″ ) Slave inverter follows the rotation direction of the Master inverter and its position. There’s no possibility of switching the direction of the Slave inverter (Master run forward and Slave run in reverse) other than electrically switching the A and B phases together.

To allow for control of direction, there’s the possibility to use PULSE/SIGN input mode in the Slave inverter. Using this method, you need to remember that the Slave inverter can no longer follow the direction of rotation of the Master inverter, but can only follow its position. So when the Master inverter changes its direction, the Slave will still rotate in the same direction, synchronising with pulses from the Master inverter.  Keeping that in mind, direction control needs to be executed externally, for example, by a PLC.

1. Pulse signal type

The standard signal when using an A8AL pulse train input signal from another A800 inverter is a two-phase pulse train like the one below:

( Pr.428=”5″ )

To allow for changing direction without changing A and B phases together, we will use PULSE/SIGN mode with only the A phase:

( Pr.428=”1″ or “4” )

But it would be best if you remembered that the inverter is counting both leading and falling edges in a standard signal, so when you switch to PULSE/SIGN type, the Slave inverter will rotate 4 times slower than the Master. To even the speed of the Master and Slave, you will need to set up an electronic gear in the Slave inverter that will multiply 4 times the incoming pulses.

2. Wiring

To use PULSE/SIGN mode, you need to connect the A-phase from the Master and NP signal, like below:

(A8AP can also be used on the Master side)

3. Electronic gear 

To ensure that pulses from the Master inverter are correctly interpreted, you need to set the electronic gear with a 4/1 ratio. So Pr.420 should be changed to “4” and Pr.421 should remain at “1”.

4. Changing direction

To change the direction value of Pr.428 should be changed between “1” and “4”. Changing this parameter changes the logic of NP input:

Change of direction is possible during rotation, but you need to remember that the motor will change its speed without any ramp, so overload might occur.