Jigar Shah
Member
I am using a 1762-L32BXB for a smiple application to vary the speed of a VFD via Modbus.
I have used a STI in the program wherein I Reduce/Increase the speed of the VFD at set time intervals and another SBR wherein I calculate the Increment or Decrement Factor.
The Speed of the VFD is varied as per the RampUp or RampDown time.
For Example,
VFD is at 100Hz with a Ramp Down time of 20seconds. Ideally, if I keep the Down button pressed for 15 seconds, the VFD should come down to 25Hz from 100Hz. In my case, it comes down only to 27Hz, there is an error of 2Hz somewhere.
I decrement the frequency on the call of an STI. The decrement factor is calculated as:
((MaxHz - MinHz(0 in this case))/(RampDown Time(Secs) * 1000) * Interrupt time)
I put this on the PLC and a timer with base 0.001 for 15 seconds to get the frequency down, that's when I discovered the error.
I couldn't figure out what is going wrong and where, any pointers would be helpful. Kindly find the attached sample program for reference.
I have used a STI in the program wherein I Reduce/Increase the speed of the VFD at set time intervals and another SBR wherein I calculate the Increment or Decrement Factor.
The Speed of the VFD is varied as per the RampUp or RampDown time.
For Example,
VFD is at 100Hz with a Ramp Down time of 20seconds. Ideally, if I keep the Down button pressed for 15 seconds, the VFD should come down to 25Hz from 100Hz. In my case, it comes down only to 27Hz, there is an error of 2Hz somewhere.
I decrement the frequency on the call of an STI. The decrement factor is calculated as:
((MaxHz - MinHz(0 in this case))/(RampDown Time(Secs) * 1000) * Interrupt time)
I put this on the PLC and a timer with base 0.001 for 15 seconds to get the frequency down, that's when I discovered the error.
I couldn't figure out what is going wrong and where, any pointers would be helpful. Kindly find the attached sample program for reference.
