What might be the symptoms if a PLC isn't generating speed signal to frequency drive?

[phatcreators]

What might be the symptoms if a PLC isn't generating speed signal / speed command / reference to the frequency drive ?

which is subjected to run a 3 phase squirrel cage induction motor ......

 

[D.A.(Tony)Stewart]

1. CMOS latchup from ESD event (a.k.a. EOS event)
2. NOP loop waiting for IRQ
3. No sign of life in sanity timer output ( bad design)
4. no self monitor for reliability of PLC . auto self-test... auto check feedback loop
5. fried PLC from back EMF and lack of protection
6. least likely defective part ( unless blown from failure to recognize risks and design protection)
7. most likely defective EMC design.

 

[munzir]

how to figure it out that the problem lies inside the PLC or in its module ?

 

[D.A.(Tony)Stewart]

Typical debug skills doing mental transfer function on each component. Output vs input. for both current and voltage.. Also back drive outputs to see if active using 1KΩ or whatever to pull up down. It's all an application of Ohm's Law and understanding specs for system and parts.

 

[munzir]

can i measure that frequency reference with a DMM in DC volts range ?

 

[phatcreators]

shouldn't there be no rotation or no torque if the signal is not given to the drive by the PLC ?

 

[dineshdeshmuk]

If the Run command indication on the drive is lit continuously and the stop command indication on the drive blinks at the same time , then what could be the cause of the problem ?

 

[D.A.(Tony)Stewart]

can i measure that frequency reference with a DMM in DC volts range ?

Yes if the output is a one shot pulse for each rev. (same as a tach)

 

[phatcreators]

i measure the DC volts when it was running perfectly before the problem occurs , the DC volts keep on increasing from 0.35 Vdc to about 3.65 Vdc .......... from the slowest to the fastest speed of the machine

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i measure the DC volts when it was running perfectly before the problem occurs , the DC volts keep on increasing from 0.35 Vdc to about 3.65 Vdc .......... from the slowest to the fastest speed of the machine

 

[dineshdeshmuk]

If the Run command indication on the drive is lit continuously and the stop command indication on the drive blinks at the same time , then what could be the cause of the problem ?

 

[munzir]

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