powerflex 700 without vector control

Hi guys,


I am trying to setup a 4 - 20 mA analog output from the POWER FLEX 700 drive ( terminals 8 and 9) to an analog input card of a PLC (it accepts 4- 20 ma) which inturn sends a corresponding signal to display cartons/ min on a computer screen but my problem is that when the drive is running at the set frequency ( 42 hz) the cartons /min shown are way higher than they should be. Is it possible to limit the output current from the VFD so that the carton counter is no more that 70 cartons/ min. I mean can it be scaled. If yes then is it possible only on a Allen Bradley vfd with a vector control option or a standard option will also do it.

pl advice.

regards

kanwar

What parameter are you sending to the analog output?

How are you getting the carton count in the PLC?

Analog output 1 sel parameter 342

Analog Out1 Hi 343

Analog output 1 lo 344

i forgot to mention that 4- 20 ma output from the vfd is fed to modicon analog input card which in turn is shown as a carton count on the screen. The screen shows 103 when ever the drive is running at the set frequency of 42 hz. This figure 103 decreases as the frequency of the drive is reduced.

So you have P342 set to 0 (output freq).

If your carton count is going up and down with the frequency, and the value is not what you want you need to have a look at how it is scaled in the PLC, you need to look at the raw value and how the PLC turns that value to a carton count.

What values do you have in P343 and 344, this will determine your output current.

P343 should be set to 20 and P344 should be set to 4.

Also bit 0 of P340 should be set to 1 for current output.

So you have P342 set to 0 (output freq).

If your carton count is going up and down with the frequency, and the value is not what you want you need to have a look at how it is scaled in the PLC, you need to look at the raw value and how the PLC turns that value to a carton count.

What values do you have in P343 and 344, this will determine your output current.

P343 should be set to 20 and P344 should be set to 4.

Also bit 0 of P340 should be set to 1 for current output.

Click to expand...

Darn. Finally something I knew, and I'm too late.

thanks for the response. Do you think the output mA from the powwerflex can be limited to a max value no matter what the higher value be so that the final displayed value on the screen can be limited to 75 instead of 103.

thanks

yam785 said:

Darn. Finally something I knew, and I'm too late.

Click to expand...

thanks for the response. Do you think the output mA from the powwerflex can be limited to a max value no matter what the higher value be so that the final displayed value on the screen can be limited to 75 instead of 103.

thanks

Yes. You can change the maximum output of the PF700 so that it does not put the full 20ma, you would need experiment with P343 and watch the results in your PLC/display, to set your final value for P343.

Allan,

i did try playing around the parameters but no matter what is set as long as the vfd is running at set frequency the display remains unchanged

First understand how the analog output on the powerflex works when it is set to look at output frequency.
The maximum Frequency P055 sets Upper end of the analog output.
example 1
P344 Analog Lo = 0
P343 Analog Hi = 20
P055 Max Frequency = 60
If the output frequency is at 60 analog out will be 20mA
If the output frequency is at 0 analog out will be 0mA

Example 2
P344 Analog Lo = 4
P343 Analog Hi = 20
P055 Max Frequency = 90
If the output frequency is at 90 analog out will be 20mA
If the output frequency is at 0 analog out will be 4mA

This should give a clear understanding of how the analog out works.

Now on to the input to the PLC. I am not familiar with your type of PLC but with Allen Bradley you have to look at the FULL range of mA that the analog input can accept. Because this will correspond to the full raw range value in the PLC

Example 1
Analog Input full range is 0-21mA which will represent 0-32767 in the PLC. So at 4mA we should see 6214 in the PLC and at 20mA we should see 31206 in the PLC.

Knowing how your PLC takes in the analog input you should be able to scale the analog input to a carton speed etc in the PLC

I hope at least the drive part clears some things up and the plc part will give you some things to look at.

urvinder_pal said:

Allan,

i did try playing around the parameters but no matter what is set as long as the vfd is running at set frequency the display remains unchanged

Click to expand...

First question: how are you changing speed drive, with a pot, from a plc etc ??

Second question: you say you are getting a 4-20 ma signal from the drive and connected it to the drive, are you able to see how many mAmps are you getting from the drive, and what is your scale on the plc, i.e. 4A = x counts 20mA=yy counts.

In general, it is preferred to use the full range of drive output and also the full range of PLC input and do the math inside the PLC to get a display of cartons per minute, widgets per day, feet per second, or whatever speed-based units you desire.

Pinching down on the drive output or the PLC input may seem like a way to accomplish the same thing but, actually, you are reducing the resolution of the communication link and therefore, the accuracy.

hello,

thanks for the information.Well i connected a digital mA meter in the output circuit to the PLC.The wire terminals on the VFD i am using are 8 and 9. The output on the digital mA when the VFD is running at the set frequency of 42 Hz is 20.00 mA and if the VFD is not running the mA output reduces to 17 mA. I changed P055 from 100 Hz to other different values but nothing changes.Also i can adjust P344

hello,

thanks for the information.Well i connected a digital mA meter in the output circuit to the PLC.The wire terminals on the VFD i am using are 8 and 9. The output on the digital mA when the VFD is running at the set frequency of 42 Hz is 20.00 mA and if the VFD is not running the mA output reduces to 17 mA. I changed P055 from 100 Hz to other different values but nothing changes.Also i can adjust P344 any value but somehow the VFD does not allow me to change the P343 value. Is it possible that some other parameter needs to be adjusted.P344 (analog output 1 low)AND P343 (analog output HI) are 4 mA and 0 m A respectively.

Yes the speed of the machine is being controlled from an external POT.Pl advice further.