• 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 synchronization to pulses from the Master inverter.

A general description of Master-Slave synchronization of FR-A800 inverters with wiring diagrams and parametrization 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 synchronization ( Pr.419=”1″ ) Slave inverter follows the rotation direction of the Master inverter and it’s 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 only can follow its position. So when the Master inverter changes its direction, the Slave will still rotate in the same direction, synchronizing with pulses from the Master inverter.  Keeping that in mind, direction control needs to be executed externally for example by 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 A phase:

( Pr.428=”1″ or “4” )

But it would be best if you remembered that the inverter is counting both leading and falling edge in 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 Master and Slave, you will need to set up an electronic gear in the Slave inverter that will be multiplying 4 times 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 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.