Qustion about a VFD and Pressure Transmitter

Hi All,

We have a Telemecanique Altivar 61 that is attached to a pump motor that pumps water out of a creek to a center pivot. So far so good!

The old setup used a old pressure transmitter that when a certain pressure was hit (by selecting by hand) the contacts would open and drop out the contactor. This system is no longer there at all. I have a Barksdale 425N1-06 (0-200 PSIG) pressure transmitter that we are using. The way this system is set up from what I can tell is as long as there is pressure, the system will run, if it goes too low or too high (pressure of 0 or over 200) the drive stops.

My question is this; there are four different center pivots we use. They range in what pressures they can take, 125PSIG, 150PSIG, 175PSIG, 200PSIG. What would be the easiest way to setup the drive to be adjustable to the signal coming back from the pressure transmitter?

The guy who will be running this needs it simple, don't need him into the drive parameters. I was wondering could I hook up a potentiometer to the drive and allos adjustments that way or be able to program 4 different setups with a selector switch.

BTW: The drive is setup for PID tuning so it adjusts drive speed as need to maintain constant pressure.

I'm assuming that this is used in an irrigation system.

The VFD drive needs to see 4 different pressure setpoints. You need to be able to select which one of these 4 are fed into the VFD external setpoint input. The VFD will then use this signal as its setpoint for the PID control.

One solution is to install a small, inexpensive PLC to handle the front end. Something like an Automation Direct DL-05 ($100) with an analog output card. Connect a 4 position selector switch to 4 of the discrete inputs. Then wire the 4-20 mA output from the PLC to one of the analog inputs on the VFD drive. Program that analog input to act as an 'external setpoint' for the PID in the VFD. Put a small program in the PLC that will output one of four different mA outputs from the PLC (that you program into the PLC) depending on what position the selector switch is in.

Wire the pressure transmitter to one of the other analog inputs on the VFD and program it as the PID reference signal.

Quick, easy and cheap, and all the operator has to play with is the selector switch. Maybe install a 5 poition selector switch and use the 5th position for "off".

SOLUTION #2:

I thought about this over coffee. Yes you can do it with potentiometers. I would be crude, but it would work ok.

By connecting a resistor (potentiometer) in parallel across the analog input terminals to the VFD, where the pressure transmitter is connected, you can trick the VFD into thinking the pressure is different than it really is. Now if you put a switch on the potentiometer so you can switch it in and out of the circuit, you can select either of 2 "pressures". Dupplicate this 4 times and you can select any of 4 pressures.

Remember that the potentiometers will have to be all connected in parallel across the VFD input terminals, with a 4 position slector switch that would allow the operator to select any one of the 4 potentiometers.

Probably a 1000 ohm linear pot will work. Trial and error. If you are not ok with electrical theory and want to calculate the exact resistor values you can Google search Norton's Theory.

You can put the whole thing together for under $20.

Yes, its for an irragation system. The entire system was purchased from another compay. Had manual and vfd control. He has already sunk alot of money into this so I was trying to stay away from the plc area. Could one potentiometer work? Just adjust it to the desired position and go from there? He could work that out he just really doesn't want to go into drive settings (which I don't blame him).

If I could, I would go with the DL series like you were talking about, just trying to save the small farmer a little money!

If you configure the drive analog speed reference so that 20mA is 200 PSI, then each of your pressure settings is a 2 mA step down, ie
175 PSIG = 18mA
150 PSIG = 16 mA
125 PSIG = 14 mA.

It should be simple enough to have a four position switch that steps through a set of series resistances to drop the reference current by 2mA. The exact resistance values depend on your power supply voltage and drive input impedance.

ETA, a second option is to put four pots in parallel - a little more set up to do but also more flexible.
.

I'm not familiar with your drive. Does it have programmable inputs?

Many do, and you can just wire a selector switch right to the inputs, set up 4 pressures in the parameters (one time by you, not him) and then the farmer can just select the switch position that applies.

I work a lot with Hitachi VFDs and that would be a piece of cake.

Short of that capability, I agree with the idea of the cheapest available PLC with an analog output, inserted at the front end.

Just be sure the drive can handle 2 analog inputs, one from the transducer, and one from the PLC.

Stationmaster

After alot of reading and thinking on the situation and speaking with a rep from the company that built the panel, I am going to wire a pot into the analog input and set the pid to look at that input for the pressure setting. This seems to be the quickest and simplest way..I'll let you know how it works out! Thanks for everyone input.

This is the 1st time I've worked with the Ativar 61 as well, I am more of a PowerFlex guy, so its good to learn new things. Programming manual is a little big

Check out page 146 in this manual:


http://www.global-download.schneide...780035E56F/$File/atv61_programming_manual.pdf

I didn't read very much of it, but it looks like it's what you're after if I understand you correctly.

ATV61 PID Preset References

As Jesper pointed out, the ATV61 can have 4 preset PID references programmed into it. Two digital inputs are required to switch between the different presets. The two inputs follow a binary pattern for selecting the reference.

Read the manual in the link in Jesper's post for more information.

OK so you have 4 crop circle sprinkler rigs.
"125PSIG, 150PSIG, 175PSIG, 200PSIG.
Are these the inlet pressures for the four units or are they the pump discharge pressure which varies with piping length.

Is the flow rating of each the same?
IF so would it be easier to measure flow? Granted that takes you into another realm of sensor with other complexities and ADDED COST - but pump speed would only need to be controlled for just one sensor and you would not have to do all this variation.

The other thing that comes to mind - how do you turn water on to each one - manual valve? If electric - then you could select a valve and matching sensor whose output goes to VFD. More bucks I know.

Dan Bentler

Actually its only a one crop sprinkler rig. What changes is the rig itself (moveable to different farms). Depending on which one is there at the time is the need for the different pressure settings.

It will be difficult to set a physical potentiometer at exactly the point needed to produce the desired pressure. You may have a few blow-outs from putting too much pressure on a rig not rated for that range. Some drives have a "digital" pot that can be set exactly and the display shows what the pot is set at. This would be much easier to set, but the farmer would have to be taught how to do it.

It would be much more reliable (and simpler for the user) to program the drive internally to have 4 setpoints, then install some type of physical selector switch, so the farmer selects 1, 2, 3, or 4, in order of low to higher pressure. If your drive has a HMI interface, then you may be able to use the built-in keys to enter the switch settings.

As Jesper pointed out, the ATV61 can have 4 preset PID references programmed into it. Two digital inputs are required to switch between the different presets. The two inputs follow a binary pattern for selecting the reference.

Click to expand...

In which case you probably can install a thumbwheel switch, and use the first 4 numbers to set the two digital inputs.

i need help

hi
i have a altivar 61 and an anlogue pressure transmitter i want the analogue switch to send the analogue signal refering to the pressure to the VFD and i want the drive to adjust the frequency automatic and adjust the pressure online on a constant value .
so i have a pipe line and i want the pressure to be constant on 6 bar , i will install an analogue switch and connect it to the analogue input to the VFD i want the drive to adjust yhe frequency by itself to maintain the pressure on 6 bar
how can i connect the transmitter to the drive
i also tried the PID

How can I connect the transmitter to the drive ?

Click to expand...

Haneyezzat,
Connect the transmitter to the drive very carefully!

If it is a voltage output transmitter, you can connect it to the Altivar 61 Control terminals A11 and COM (0 volts). See the attached picture. Terminal A11 can only be programmed as a voltage input terminal. If your transmitter has a current output, you can connect it to terminals A12 and COM. These terminals can be programmed as voltage or current input terminals.

You need to get copies of both the Altivar 61 Installation Manual, and the Programming Manual. There are many parameters (over 500), and most of them have to be set correctly for your specific installation. I recommend that you read the Programming manual until you understand how the Altivar 61 programming Parameters are organized, how they work, and how to change them. You should keep a record of the ones you change, and what you set each one for. User Setting Table forms are provided in the back of the Altivar 61 Programming Mannual, page 223.

You will need to change the Speed Reference parameter Fr1 to select the analog input as the speed reference that you want to use. If you want to have more than one speed reference under different circumstances (loss of the signal), there are provisions for programming that situation also.

Here is a list of only a few of the Parameters that I know you will need to check and probably change from the default setting:

Pid PID regulated. There are many other related parameters to set up the PID function.
bfr Standard motor frequency
nPr Rated motor power
UnS Rated motor volts
nCr Rated motor current
FrS Rated motor frequency
nSP Rated motor speed
EFr Max Frequency
IEH Motor thermal current

Fr1 Reference 1 channel <--- This one is important to change where the speed setpoint comes from. You probably will want to change to A12 for a current input from your transmitter.

rIn Reverse Inhibition (default "NO"). For a pump, be sure to set this to "YES".

CCS Command switching. Default is Channel 1 active. If you want to allow more than one way to control the drive speed, this and the following 5 parameters on page 109 is where you do that.