# Positioner to vfd 4-20ma



## yawaryounited (Mar 6, 2018)

Hi Goodevening folks i would like to ask 

How would i connect my positioner transmitter to my VFD (TECO A510 SERIES)

The positioner is for high and low level purposes when there is change of degrees of opening in the positioner it will send feedback to the VFD varrying the speed of the motor depending on the ° of opening 

* how would i test to have accurate 4-20ma output without using fluke process meter?

how would i set or configure the positioner that when it has 60° opening it will automatically adjust the vfd frequency .

for example vfd max is 60hz and vfd min is 20hz
if it has 60°opening frequency should be varry from previous to the corresponding freq base on the opening .


for its circuit

Positioner Transmitter > Amplifier > Sipart D21 > VFD

can i bypass the sipart and from amplifier it will directly send feedback to the vfd from the positioner?


THANKS AND GOD BLESS


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## MDShunk (Jan 7, 2007)

Run your 4-20 level sensor into a 0-10v signal conditioner then bring that 0-10v right into the vfd. Some people might use a 500ohm resistor, but a signal conditioner is better. They're cheap enough. 

I didn't look up your particular vfd, but I assume it has 0-10v control capability like every other vfd on earth.

No need to run it though the Sipart UNLESS you want PID control. That is, do you want the motor to maintain a stable level, or do you truly want it to truly follow that 4-20 input signal?


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## MDShunk (Jan 7, 2007)

I couldn't help myself. I looked up your drive manual. Your analog input #2 on that drive will take 4-20 directly AND your drive has a PID control function built in. You can do it all by connecting sensor to drive, then program accordingly. Should be a dirt simple setup.


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## MDShunk (Jan 7, 2007)

I'd probably fudge the zero and span on the positioner transmitter to output from 60 to 100 instead of 0 to 100 to keep your desired control scheme in tact. Set the min speed parameter on the VFD at whatever you want it to run at from 0-60 degrees of damper opening, then the 4-10ma input will ramp it up from there. There's a million ways to do this. That's just the first one that popped in my head. 

Just put your meter in milliamp mode and check the output of your transmitter by breaking one line- same as you'd measure amps on anything. No need for a process calibrator. This isn't a petrochemical plant. It sounds more like you're working on an air handler of some sort.


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## tates1882 (Sep 3, 2010)

Depending on the application, the PID loop will definalay need to be calibrated, I've never been able to use the factory settings without adjusting PID ramp times to avoid over modulation.


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## MDShunk (Jan 7, 2007)

tates1882 said:


> Depending on the application, the PID loop will definalay need to be calibrated, I've never been able to use the factory settings without adjusting PID ramp times to avoid over modulation.


I'm not sure how fast his damper position moves. He may not even need PID control. 

Calibrated might not be the right word, necessarily. Tuned is the word more typically used. For something as simple as an air handler, a fella could just monkey around with P, I, and D for a little bit and come up with something reasonable.


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## Rora (Jan 31, 2017)

Set up your zero and span frequencies on the VFD, connect the transmitter 4-20mA output directly to the analog in. Move the positioner to the desired low and high positions then adjust the zero and span trim on the transmitter until you get the desired frequency output on the VFD for each position (or mA reading that is based on, if your VFD shows that). Regardless of the actual current value, this should correlate the 4-20mA as the VFD measures it to the associated position. Be sure to repeat the zero-span trim adjustment a couple times (zero-span, repeat until consistent).

As far as controller action, understand that what you're describing is essentially proportional-only control--the change in VFD output is directly proportional to the change in 4-20mA input from the transmitter. Integral and derivative action are additional parameters that can be used to provide better performance (integral ensures more precise adherence to a desired operating point, derivative decreases the amount of time required to reach a desired operating point).

Whether you need integral action depends on how precise the feedback relationship is... if 40 Hz doesn't precisely maintain the positioner at the middle position, then your steady state will have persistent offset--that is, the VFD will output 40 Hz but the position won't be exactly in the middle. An offset will be present regardless of the operating point, 50% is just for example.

Whether you need derivative action depends on how quickly the position may be changing, if there are large changes of position in a short span of time then the VFD's response may not be dramatic enough to maintain stable control. If the feedback is too noisy (sharp changes of small magnitude), that will actually decrease stability with derivative action.

It all depends on the behavior. Does a change in VFD output result in a quick response in the position feedback? If so, you probably don't need derivative action. Is it unimportant to operate without an offset, or will the position feedback perform precisely enough that the two can remain balanced to your liking without offset correction? Then you probably don't need integral action. I'd suggest starting with P-only and adding I and/or D action if you experience any of these issues.


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## yawaryounited (Mar 6, 2018)

@MDShunk @Rora

look at the attached pic below 
how will i remove the sipart or bypass it

can you improvise its connections ?

can you explain it to me the ckt diagram thanks alot


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## Rora (Jan 31, 2017)

Appears your VFD takes the 4-20mA feedback on pins 34/35. The "AUTO/MAN CONTROL" selects between completing the loop either through the SIPART DR-21 (automatic) or the KFD2-PT which takes a potentiometer (dial) input and generates the 4-20mA (manual). Not sure how familiar you are with control loops, but the SIPART will adjust the 4-20mA going to your VFD to try and match the position feedback with an adjustable setpoint, the KFD2-PT will adjust the 4-20mA to the VFD based on a dial so you can directly control VFD output and ignore position feedback.

The question though is why you want to bypass the SIPART? You'd have to adjust your setpoint (automatic) or set frequency (manual) right on the VFD. Gotta consider whether you really want to be operating the loop from the VFD rather than something that can be panel mounted. It's possible, just not something you'd typically do.

Either way, all you'd be doing it getting rid of the SIPART DR-21 and KFD2-PT, and take the "4-20 ma" feedback from LTZN7 pins 31/32 and go directly to the VFD pins 34/35 (you can see it takes the same 4-20mA from the removed components), then performing auto/manual control on the VFD.


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## yawaryounited (Mar 6, 2018)

@Rora thank you for that sir
look at the pic i attached from what i have understand is it right ?

if i get rid of the sipart d21 should i also get rid of the potentiometer ?


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## Rora (Jan 31, 2017)

You could do it that way if you want to keep the potentiometer/dial for manual control instead of doing it on the VFD (one issue with the wiring, though, see below). However, you'd have to change the settings in the VFD any time you want to switch to manual/dial control since the signal you'd be sending is what you want to directly drive the VFD at rather than a feedback signal for automatic control.

If the VFD is set up to run in automatic with feedback from the positioner and you send it a manual signal from the dial, it will be changing the frequency output in order to influence what it thinks is feedback, but without any ability to do so, so it won't work correctly. Especially if integral action is used, the output will ramp to either it's min or max in order to eliminate an offset in the feedback that it can't eliminate.

There is a wiring issue with the 2nd drawing--you can't have the positive from the positioner feedback and potentiometer/dial common to each other. If you look at the original drawing, only the negative is common (LTZN7 pin 32, KFD2 pin 8, VFD pin 35), the positive go through the AUTO/MAN selector. To switch between AUTO/MAN you'd have to change the selector as well as change the VFD settings between automatic control and direct drive.

Another option you may consider is using the dial as a setpoint/reference adjustment instead, which would be wired to the other analog input and get rid of the selector. Only analog input #2 is 4-20mA, #1 is 0-10V, but it seems the KFD2 is actually a 0-10V output so that would work well. Then you could leave it in auto mode and would only have to change something on the VFD if you wanted to directly adjust the frequency output, it'd have to be controlled on the VFD at that point.

3rd and simplest option is to just get rid of the dial and selector switch too, run in auto, adjust setpoint/reference on VFD, and run manual/adjust frequency directly on the VFD if you ever need to.


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