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Old November 8th, 2018, 06:03 PM   #16
OkiePC
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I had to write code for a system with multiple storage tanks, pump stations at various elevations, some of which feed each other, and there were valves. It was a little bit tricky to control everything right and not overpressure certain lines. I had to have different setpoints for the pressure target at one pump station depending on how many valves downstream were open, and I had to have a really long ramp up time (4-6 minutes) during which I ramped the pressure setpoint from the minimum entry to the presently selected target. I also had to condition the logic with the measured flow with shutdown alarm settings for high or low flow. So at least if a line did break, or if a valve stuck shut, the out of range flow rate should indicate that. I was lucky in that the system operator had a good handle on how everything should work, but there were still things that were in his head that didn't quite jive with reality, so a few things had to be edited after commissioning to get it all smoothed out.

The better handle you can get on how the system is laid out up front the better. I highly recommend studying any drawings that exist and creating at least a good sketch if there aren't any or if they are inaccurate.
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Old November 15th, 2018, 12:16 PM   #17
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Thanks everyone for the replies so far. I went over there and go some more information on the system. Though I didn't start changing setpoints as I didn't have an operator there, I did get some information on the pumps / motors / etc. I'm going over there next week to tune in the PID loop. I'm being assured that when they "make adjustments" on the system that they are changing the VFD frequency rather than the pressure setpoint. I'm taking that information with a grain of salt until I verify myself.

Tom: I saw you mentioned the pump dead-heading. The thing is, I can't really see a way to get the system head with the system running and there is no documentation for that parameter of the system.

I've also read that a lot of times the system can be used on just PI control. What I'm worried about is a pressure overshoot blowing out a pipe some where while I'm tuning the loop in. Thoughts on this?

There is a pipe going into the cistern with a valve. The wires coming from the valve have been cut, and it looks to me to be a high pressure bypass. If you shouldn't have backflow in the system, is this return line not backflow? It appears to me to be a pressure relief valve, and I feel that it needs to be in the system.

There are two drives. These are both Altivar 21 drives. Both motors are 7.5 HP but there is one 15HP and one 7.5 HP drive. I have no clue why that is, and I see a couple possibilities, but they will end up being replaced.

Also, I've checked in to see if there is any kind of regulatory issues with me taking on the job, and there don't seem to be any. I'll post a few pictures here of some of the gems I have found so far. The two main ones being that all materials used were standard household materials, including the 200A 3ph panel delivering power to the system. Also, the PLC cabinet is used as a pull box for a lot of lighting and power circuits. I've told them that this will have to be changed before we touch the system. There are also lots of code issues that need to be addressed, such as no disconnects on the load side of the VFDs. Also, check out the bus bars on that non-rated panel.

https://imgur.com/a/cFFnGXH

Last edited by sparkie; November 15th, 2018 at 12:23 PM.
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Old November 15th, 2018, 12:44 PM   #18
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Quote:
Originally Posted by sparkie View Post

There are two drives. These are both Altivar 21 drives. Both motors are 7.5 HP but there is one 15HP and one 7.5 HP drive. I have no clue why that is, and I see a couple possibilities, but they will end up being replaced.

https://imgur.com/a/cFFnGXH
Usually doubling the HP of a drive in comparison to the motor (especially in this application) means that they are using a phase conversion from three to single. Not sure why they would do that on just a single drive though...
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Old November 15th, 2018, 12:51 PM   #19
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Quote:
Originally Posted by sparkie View Post
...Also, check out the bus bars on that non-rated panel.

https://imgur.com/a/cFFnGXH
Is that a bleach pump in the 4th pic?

If so, that is probably why the bus bars look like they do, and why there is green life growing on all the copper.

Every day working in the water industry, I thank God for my personal well. I tell everyone who will listen, "whatever you are paying for water, it isn't nearly enough." I have pictures like yours and much worse to drive home that point.
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Old November 15th, 2018, 01:07 PM   #20
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First thing if they are truly setting the VFD frequency to regulate pressure then I can see why they are blowing pipes. The only way to control system pressure would be to control the discharge. Open or close the valves. Close all the valves then pressure will go overshoot big time enough to blow the piping that would also explain the bypass valve returning back to the tank that has the wires cut. As the pressure goes up open the bypass valve to return the water to the tank in this case the valve can’t work to relieve the pressure as the downstream valves close the pressure goes up pipes blow
As for the 7.5 hp motors and one 15 hp vfd and one 7.5 hp vfd it look like at some point they tried to save a few dollars and use one 15hp vfd driving both motors together but the soon figured out that didn’t work for them and just added the 2nd vfd and split the motors.

The controls for this system need to completely redesigned from the ground up or they will continue to have problems.
They should be controlling the system pressure using pressure transducer feedback controlling the vfd speed as well as stagger the operation of the pumps and run times eliminate the bypass valve it’s not needed with a vfd system it was most likely a holdover from when the pumps were on line starters

By the way this could be done without a plc just using the vfd's
it would be a nice little project to do

Last edited by GaryS; November 15th, 2018 at 01:13 PM.
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Old November 15th, 2018, 01:14 PM   #21
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First thing if they are truly setting the VFD frequency to regulate pressure then I can see why they are blowing pipes. The only way to control system pressure would be to control the discharge. Open or close the valves. Close all the valves then pressure will go overshoot big time enough to blow the piping that would also explain the bypass valve returning back to the tank that has the wires cut. As the pressure goes up open the bypass valve to return the water to the tank in this case the valve canít work to relieve the pressure as the downstream valves close the pressure goes up pipes blow
As for the 7.5 hp motors and one 15 hp vfd and one 7.5 hp vfd it look like at some point they tried to save a few dollars and use one 15hp vfd driving both motors together but the soon figured out that didnít work for them and just added the 2nd vfd and split the motors.

The controls for this system need to completely redesigned from the ground up or they will continue to have problems.
They should be controlling the system pressure using pressure transducer feedback controlling the vfd speed as well as stagger the operation of the pumps and run times eliminate the bypass valve itís not needed with a vfd system it was most likely a holdover from when the pumps were on line starters
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Old November 15th, 2018, 01:53 PM   #22
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OkiePC, yea that is chlorine. There is a LOT of condensation in the pump house on the walls from when I went there the other day. There is an exhaust fan on a switch as well. I tested it and it works. I'm going to just put it on a humidistat so it turns on when it needs to exhaust excess moisture. This entire setup was done with non-rated materials for the environment. The 4-20mA control loop coming from the transducer has 3-4 devices in the loop. Once tuned it properly, I see no reason why this wouldn't work, but I'm not a fan of the method. They also have the VFD lines/loads, 24V control wire and 4-20mA sensor wire all in the same conduit. The nipple is just at 24", but it still makes me uneasy, and overall just poor craftsmanship. Of course I'm going to be frugal, but I'm not interested in touching this system and following this same path.

Good observations Gary. See, I'm thinking that pressure bypass needs to be there regardless. If for some reason the system overshoots, it needs to be able to dump some of that water. It is a system return line. What I'm wondering, though, is how does having that return line affect the requirement that the system has no backflow for sanitary reasons. Also, I'm of the opinion as well, that there is one large VFD because they tried to just run both pumps on a single VFD, then they realized that this was not effective. The second pump kicks on when the pressure drops to a certain point, but there is no way to set that point.

They want remote access and monitoring in this system. I'm going to put in a cellular device to provide that connectivity and give the alarming. Because of this, putting everything on a PLC will simplify the system. Also, the motors are three phase motors, not single phase motors. I'm starting to see why the last guy to quote them on a price never got back with the on a time to do the job. It is going to take proper planning to pull this one off, which I'm not worried about once I understand a bit more about the control loop with the pumps and the line pressure of the system. I've always just had pumps that ran on starters rather than a VFD in a control loop. I'm a bit concerned about getting in the proper coefficients for the P-I-D.
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Old November 15th, 2018, 02:07 PM   #23
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Since there is a need for a PLC, I would consider bringing in the humidity too and let the PLC run the exhaust fan. Then you can run the fan on a periodic basis whether the humidity is high or not and that can help a great deal getting the CL2 out of the room. Also, you can report the humidity back to them. We have a couple of sites where they have humidity monitoring and they can tell right away when a pump seal is leaking if there is a spike in the trend not due to weather.

If you put the pressure sensors in the PLC and let the PLC run the VFD command, there are more advantages than disadvantages in my opinion. The big disadvantage is that if the PLC goes kaput, then you can't run the VFD in hand with pressure control. The advantages include being able to do whatever your imagination conceives with the pump speed. You could limit the pressure command, use steps to incrementally raise it, the sky is the limit.

I would not be surprised if you could go tweak some settings, validate the sensor wiring and make the junk behave with just a few hours time on site. I have seen situations like this. One place had replaced a 150psi sensor with a 200psi sensor and didn't "tell the drive" so yeah, it was running way too high. They also had a faulty gauge so it was not obvious. Another site was all wired right and the VFD was programmed right, but it was in the wrong mode so running at a fixed speed instead of using the sensor.

I like to use Micrologix PLCs with the 1761-NC01 board and Modbus comms to the drives. Then you can tell if the keypad is in auto or hand mode, monitor motor current, and everything else about the drive you might want. This may not seem important but will pay off when they call you in the middle of the night and you can log into their office or look at a picture of a screen with drive details to tell you what is really going on without taking a road trip. It also can cost less in hardware than analog signals and make wiring very simple.

The PID programming and adjustment for pressure control with the sensor on the discharge is not terribly challenging, so the risk of overshooting is low if you cover all your bases not the least of which is detecting a failure of the sensor. With that said, I have seen every possible mode of failure of pressure sensors in the last year. I have one I keep on the bench that puts out 20.5 milliamps at all times. I have another one that "froze" at 16.5mA. Programming to detect these possibilities is a good idea.

Also, I think I saw check valves in the pictures on the pump discharge lines, so (if they are working) that should prevent backdriving the pumps and backflow into the sump.

One more thing, in rooms with chemicals, especially CL2, I try to use poly or fiberglass enclosures. I have had great service and pricing from Wistex for boxes up to 20 x 16 which is adequate for many of my small PLC/RTU panels.

https://www.wistexllc.com/enclosures...-assembly.html
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Last edited by OkiePC; November 15th, 2018 at 02:16 PM.
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Old November 15th, 2018, 02:32 PM   #24
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Quote:
Originally Posted by OkiePC View Post
Since there is a need for a PLC, I would consider bringing in the humidity too and let the PLC run the exhaust fan. Then you can run the fan on a periodic basis whether the humidity is high or not and that can help a great deal getting the CL2 out of the room. Also, you can report the humidity back to them. We have a couple of sites where they have humidity monitoring and they can tell right away when a pump seal is leaking if there is a spike in the trend not due to weather.

If you put the pressure sensors in the PLC and let the PLC run the VFD command, there are more advantages than disadvantages in my opinion. The big disadvantage is that if the PLC goes kaput, then you can't run the VFD in hand with pressure control. The advantages include being able to do whatever your imagination conceives with the pump speed. You could limit the pressure command, use steps to incrementally raise it, the sky is the limit.

I would not be surprised if you could go tweak some settings, validate the sensor wiring and make the junk behave with just a few hours time on site. I have seen situations like this. One place had replaced a 150psi sensor with a 200psi sensor and didn't "tell the drive" so yeah, it was running way too high. They also had a faulty gauge so it was not obvious. Another site was all wired right and the VFD was programmed right, but it was in the wrong mode so running at a fixed speed instead of using the sensor.

I like to use Micrologix PLCs with the 1761-NC01 board and Modbus comms to the drives. Then you can tell if the keypad is in auto or hand mode, monitor motor current, and everything else about the drive you might want. This may not seem important but will pay off when they call you in the middle of the night and you can log into their office or look at a picture of a screen with drive details to tell you what is really going on without taking a road trip. It also can cost less in hardware than analog signals and make wiring very simple.

The PID programming and adjustment for pressure control with the sensor on the discharge is not terribly challenging, so the risk of overshooting is low if you cover all your bases not the least of which is detecting a failure of the sensor. With that said, I have seen every possible mode of failure of pressure sensors in the last year. I have one I keep on the bench that puts out 20.5 milliamps at all times. I have another one that "froze" at 16.5mA. Programming to detect these possibilities is a good idea.

Also, I think I saw check valves in the pictures on the pump discharge lines, so (if they are working) that should prevent backdriving the pumps and backflow into the sump.

One more thing, in rooms with chemicals, especially CL2, I try to use poly or fiberglass enclosures. I have had great service and pricing from Wistex for boxes up to 20 x 16 which is adequate for many of my small PLC/RTU panels.

https://www.wistexllc.com/enclosures...-assembly.html
Thanks for those tips. I'm all-to-aware of caustics and their impact on electrical equipment. The fiberglass enclosures are fantastic for anywhere there isn't going to be a lot of abuse, and much cheaper than stainless. For cost reasons, I'm going to keep this system as a PLC-only system with no hand mode. This will eliminate some push buttons and such too. I think I'll probably go with a P2k system in here again. I really liked the last one I put in. If they want to spring for a hardwired backup system, that can be done too, in the same panel.

I'm thinking eaton drives as they are stocked and locally available. As far as networking, I'm going to use ethernet as the electrical standard. As I'm going to be putting in networking capability, I might as well just save myself some IO wiring. Plus, I've found that even general use ethernet hardware tends to do really well in tough environments, think packing plant stuff. Caustic, hot, cold, humid, any harsh environment you can imagine.
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Old November 15th, 2018, 03:41 PM   #25
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The P2K can do Modbus even better than the 1400 and doesn't need the breakout board for RS485. I have one doing MRX/MRW to Yaskawa VFDs and it is nice. One twisted pair and some relatively easy keyboard magic gets you all the data both ways. I did have a serial port failure on that system and had to replace the CPU, but the RS485 wire was buried 700' to the pump house and took a lightning hit. I installed a comm port isolator along with the new CPU, but for local wiring, you may not need that extra precaution.
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Old November 15th, 2018, 03:53 PM   #26
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I will say it again this is one project you do not need a PLC.
it can be should be done with the vfd's and pressure transducers
but if you have chlorine you have other problems to deal with as well
On breath of chlorine gas can kill you do not take any chances
also you should put the controls in a separate room to avoid the humidity problem

if you have the vfd's set up correctly you will never need to open the bypass valve
As for backflow tats a relatively new thing for that you must install a backflow check valve in discharge pipe and it should be install at each point of use they should be already installed to prevent contamination check the regulation that apply in your area
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Old November 15th, 2018, 09:33 PM   #27
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Quote:
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I will say it again this is one project you do not need a PLC.
it can be should be done with the vfd's and pressure transducers
How do you handle this Gary?

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They want remote access and monitoring in this system
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Old November 15th, 2018, 10:10 PM   #28
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I am back again
the short answer is just do it
actually there many ways to remote access them
Install an ethernet option card
or use the built in default RS485 communication
either way if you need to check n them and maybe change the setpoint use the free supplied software.
I actually have about 30 crane drive using the default RS485 communication with a long range radio modems it been running that way for many years
if I remember I used about 10 radio modems on that project
it's not difficult just a little planning
if you want details feel free to PM me ill get back to you on that.

Last edited by GaryS; November 15th, 2018 at 10:18 PM.
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Old November 16th, 2018, 04:19 PM   #29
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Here is a link I think you will find interesting
This is exactly what you need

https://www.yaskawa.com/products/dri...s/iqpump-micro

Let me know what you think
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Old November 16th, 2018, 05:59 PM   #30
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I'm with Gary on his drive choice.

We've done PID loops for water systems with many different VFD brands, I don't think you'll find one simpler than an IQPump to set up. Super easy setup with the quick start guide that comes in the box.

If you want to take it a step further, they have free Yaskawa software combined with a basic USB printer cable, you can go that route too. I'm an electrician by trade, not a programmer, and even I was able to set the software up and communicate with the drive in a few minutes.

The trending on the software looks great too, I'm itching to try and tune some loops with it.
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