PMW outputs

[Hminx]

Hi All

I recently prototyped a project using PWM outputs on a T100MD 888  to operate two actuator solenoids on a truck gearbox, this works fine but when I replaced the T100 with an FMD88-10 The PWM outputs would no longer operate correctly. The outputs control two 100amp solid state relays so they aren't overloaded,  I tried another FMD88 with the same result.

Cheers Pete

[support]

It wasn't very clear what you meant by "no longer operate correctly"?  Do you have an oscilloscope to check the output waveform for frequency and duty cycle?

Note that if you are driving the input transmitter of a solid state relay, then check that the anode of the SSR is connected to the +24VDC of the PLC's power supply and the cathode is connected to the FMD PLC's digital output.

Is the SSR driving a DC load up to 100A? Please ensure that the correct type of SSR is being used.

The FMD PLC can operate a wide range of PWM waveform frequency. The T100MD is a very old PLC that only supports a handful of PWM output frequency (16, 32, 63, 250, 500, 2000,
8000 and  32000 Hz) and it will always fall only into one of the available frequencies. You may want to specify the same frequency of what is available on the T100MD when testing with FMD PLC if you expect similar behavior.

[Hminx]

What I mean by  ' no longer operates correctly ' is that when I operate the T100MD 888 with custom function :-
'
            'Set up control values for side shift
            '====================================
' set pwm level for side shift function & shift to 5th 


    setPWM 1,3500,500
    delay 10
    setPWM 1,9000,500
    delay 27
    setPWM 1,0,500
    delay 10
    setPWM 1,4500,500
    delay 5
    setPWM 1,4600,500
    delay 20
    setPWM 1,0,500
    delay 10
    setPWM 1,4600,500
    delay 20
    setPWM 1,3000,500
    setPWM 2,3500,500
    delay 30
    setPWM 1,3000,500
    setPWM 2,9000,500
    delay 100
    setPWM 1,0,5500
    setPWM 2,3500,500
    delay 2000
    setPWM 1,0,500
    setPWM 2,0,500
    delay 5000

the  outputs PWM1 ( Output 7 ) & PWM2 ( Output 8 ) work correctly and  switch the SSR's as per the custom function, but if I try to use
a FMD88-10 the same outputs only give a short duration pulse if anything at all.

[support]

We have transferred a simple program based on  your code to a FMD PLC. When CR1 relay is turn on (use left mouse click during online monitoring), PWM1 and PWM2 (output 7 and did light up momentarily for duration set by your DELAY statement.

FMD PLC uses a different type of solid state output driver from T100MD888+.  Can you try to pull up the output 7 and 8 with a 1K ohm, 1/2W resistor and see if it makes a difference to the control action on your SSR.

Please also note that FMD8810 without the FRAM-RTC have some memory limitation (only DM[1] to DM[1000] are available), so make sure that it is not because your program is trying access on existent DM memory and therefore the program is not behaving as your have experienced in T100MD PLC.