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Join Date: Sep 2014
Posts: 5

Help with VDF Pump Control

09/29/2014 8:50 PM

Hi All

I am trying to keep a constant water level n a constant flow (in and out) situation using a 2ph pump and a VAT200 GE Consumer industrial VFD

http://www.gepowercontrols.com/ex/product_portfolio/control_automation/variable_speed_drives/vat200.html

I would like to use the PID function of the driver in order to keep the level constant

as a level sensor I am planing to use a eTape liquid level sensor with 4-20mA Resistance to Current Module Interface from Milonetech

http://www.milonetech.com/uploads/Chemical_eTape_Datasheet.pdf

as per http://www.milonetech.com/Purchase_eTape.html

Any suggestions, about connection ? schematic?? what I am missing?

The main sistem controler has a 0 to 10v signal I can Use to set the apropiate level to the VFD

Can this be possible ?

Thanks in advance for your Help

Claudio

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#1

Re: Help with VDF Pump Control

09/29/2014 9:58 PM

If you have an inflow, and an outflow, a simple visual examination is all that is necessary for a constant water flow.

Adjust pump speed until tank is full and outflow is what you want.

You don't need a level switch or PID.

You leave a lot of detail missing.

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#2
In reply to #1

Re: Help with VDF Pump Control

09/29/2014 10:33 PM

Thanks for your reply

Yes you are right, With some adjustement I can have both speed for the 2 preset levels I need and indicate via 0to10v from the controler the apropiate speed for the pump

but...

the water flow has some possible variation as per the following schematic

SO when ever I operate one of the vales either on the in flow of each holding tank 1 and 2 (small ones at the bottom of the picture) or on the return flow from the main tank, the level on the main tank will fluctuate...

the idea was to have it controlled by the water level sensor and let the PID of the VFD do the work

thanks

sorry for the quality of the drawing

CLaudio

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#3

Re: Help with VDF Pump Control

09/30/2014 1:31 AM

Why not just tap the large reservoir at the bottom to return to pump reservoir and let the pump run at a constant rate while using a solenoid valve to control to this return from level sensor, then feed the holding tanks from the top? Cheap and effective.

I prefer the K.I.S.S. method, can you tell

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#4

Re: Help with VDF Pump Control

09/30/2014 8:59 AM

You don't need all that if you use a weir.

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#5

Re: Help with VDF Pump Control

09/30/2014 9:01 AM

The only purpose of a tank is to allow the level to go up and down, so if you want constant level, get rid of the tank.

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#6
In reply to #5

Re: Help with VDF Pump Control

09/30/2014 10:37 PM

Thank you all

the tanks are part of a public aquarium display, so taping the tank and other simplistic options are not an acceptable solution, main pump circulation allows for proper oxigenation and detritus removal from main tank to sump where other equipment and filters will do their job.

Having TWO levels allows me to save energy during NON DISPLAY time, by lowering level and rpm

Tank is a main display and holding tanks also contain live stock,

I will start of course with simple speed setting as per first post And work my way arround depending on how daily manipulation of return valves will influence level on the main display

The idea is to guarantee perfect level for best show with minimun (optimun) energy consumption

thanks again for your input

regards

Claudio

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#7
In reply to #6

Re: Help with VDF Pump Control

09/30/2014 10:57 PM

You should have said this in the opening post.

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#11
In reply to #6

Re: Help with VDF Pump Control

10/01/2014 2:55 AM

Two weirs and a bypass valve, then. I still can't see why you need PID level.

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#8

Re: Help with VDF Pump Control

09/30/2014 11:30 PM

Lin

My basic expertice is civil engineer, but during the years I have work in a lot of electromechanical instalations, but this programming of the VFD is a little new for me

I already figured out how to set different speed with and analog signal from my main control to the VFD via 0 to 10v on the VAT200 on the AIN port (only signal avaible for use)

The VAT200 allows me of a PID reference analog input in a different port (S6/AI2) on 0 to 10v or 0 to 20 mA on 24v

The problem is that I can not figure out how to have two SET points and some of the PID configuration needed

Also any extra electronic needed for proper conection

BTW thanks for your reply

regards

btw english is NOT my main language

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#9
In reply to #8

Re: Help with VDF Pump Control

10/01/2014 12:51 AM

You have a number of factors which need addressed: 1) depth sensor gives reading 4mA (or 0V) when tank empty, 20mA (or 10V) when tank full. But drive input will use 4mA (or 0V) for zero speed, 20mA (or 10V) full speed. 2) PID control is used to adjust flow rate smoothly to avoid water hammer while arriving at set speed quickly. 3) Setting the correct speed to maintain set level will require additional processing. I would use a comparator to measure deviation from set point. You will have to measure the sensor value at the two set points to obtain values to feed one side of the comparator, and find a way to send one or the other depending on time of day. The actual depth reading is sent to the other side. Then use this variation to adjust pump speed from its set value. But, as you have a feed pipe between pump and tank, this will be quite difficult to tune for best response in every scenario.

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#14
In reply to #9

Re: Help with VDF Pump Control

10/01/2014 9:00 AM

Sounds like another opportunity for a microcontroller like an Arduino Uno ($20) use software to invert the analog in to the required analog out, add a RTC chip (3.00) to add time options. Some of the newer microcontrollers have the real time clock built in. The options available with the SOC's (system on chip's) that have been produced over the last couple of years are amazing both in terms of price and capability.

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#10
In reply to #8

Re: Help with VDF Pump Control

10/01/2014 12:56 AM

I'm not sure how, "Having TWO levels allows me to save energy during NON DISPLAY time, by lowering level and rpm" with the tank configuration you have.

You can have two levels and keep the same pump speed by having two drains with valves that control the level.

Filtration and circulation should be the deciding factor in pump speed. Level of the tank should not be controlled by pump output volume, but drain valve control.

All the levels and flows can be controlled with valving.

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#18
In reply to #8

Re: Help with VDF Pump Control

05/21/2021 11:09 AM

If the VFD does not have an easy facility to have two setpoints altered by a timeclock, then I would try a variable resistor between the level sensor and the PID volt input, variable resistor shorted out by timeclock contact when required. The resistor "in circuit" would raise the level.

The PID input of VFD will have a fixed DC resistance - adding resistor of 1% of PID input resistance raises setpoint 1%.

If it is a mA current input then the Time contact should connect a resistor in parallel with the PID input to change effective setpoint e.g. parallel resistor of value [PID input resistance x 100] raises 1%.

I realise the VFD display will not show correct level for setpoint at both contact states, but surely obvious level marks on the tanks should be the standard, not indirect electronic indication.

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#12

Re: Help with VDF Pump Control

10/01/2014 3:02 AM

You are trying to make the problem fit the preferred solution. The right thing to do is make an appropriate solution for the problem.

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#13
In reply to #12

Re: Help with VDF Pump Control

10/01/2014 6:58 AM

Ideally you want to have the level of the main tank below that of the display tanks where a weir or siphon box on each display tank could gravity drain back to the main tank. This holds the level in the display tanks at fixed level, which should be the real goal. Flow to each tank could then be regulated independently at the desired rate with manual valve positioning. The weir or siphon could also provide extra aeration and bio filtration. A pump could then pump at preset rates back to the display tanks. I might even use two pumps with the desired curves rather than a VFD, depending on the desired delta in flow rates. Be absolutely certain your design won't cause an over flow situation should a filter or valve clog. Your sketch appears to allow for that.

This is not a new problem and I'd suggest a trip to pet or aquarium shop to observe how they do it. Then focus on treatment and feed of makeup water, which adds another tank to your equation.

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#15

Re: Help with VDF Pump Control

10/01/2014 9:05 AM

What is the physical level of the main tank in respect to the other tanks and the reservoir?

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#16

Re: Help with VDF Pump Control

10/01/2014 11:40 AM

First of all

let me thank you for all your suggestions, I am going to answer all of them in order to get to a better solution

As I explained before this is a public display tank, the whole system is over 1000 gal, main tank is 660 gal and we are retrofitting it, it is an existing system we are trying to update

About the weir...

Even if for some over flow are relatively small is not the issue in this tank , the turn over rate is very high because the live stock is basically living corals (not the plastic types you see on your regular tv show)

Overflow boxes are being REMOVED, because for the size of the tank and the big turn over rate OVERFLOW BOXES (weir) are Bulky, occupy a lot of internal space, and most of all are NOISY. and we still have a big level control issue because in order to minimized we need a really huge weir in order to have a very low dinamic water above the weir. Also overflow boxes will have to be connected to the return system any way...

About valves...

yes I am using valves And I will tune them for optimal flow in all of the tanks BUT the main tank why? I have a rather over calculated return pipes to the main sump ( 2ΓΈ 3") calculated as drainage pipes (not pressure ones) my main concern here is

a) to have maximun return to sump in order to avoid pump and system failure

b) eliminating any chance that external material (fishes, crustacean dirt etc) will block return and overflow the main tank in the viewing launge

c) actually the main tank have valves controling the IN flow but a very free out flow

All other holding tanks have valves in an out in order to isolate them for maintenance, cleaning, dosing, etc

All overflows return connection of different tanks are laterally located and above a a set level in order to guarantee that in a event of power failure there is always be water in ALL of them... and the water will distribute evenly in all tanks and not over low any of them.

In this case sensors if used, will measure "O" Cero (0v or 4mv) at this minimun level and not at the bottom of the tank.

I could measure the different levels I need, and set the offset in the VFD for the direct control for example if I send 0v from the controler, the vfd will manage 60% and if a send 10 V VDF will manage 100% pump capacity THAT is CLEAR and easily done

where I am really lost is in the reference measure from the sensor to the pid input in the VFD.. and all the other parameters

Main tank return level is only 18 inches above the rest of the tanks, actually all bottoms are level, main tank is located in front, and all tanks are behind a wall at the back.

due to the size of the main tank, 6 inches in water level difference is a huge return flow difference, so by jus changing that much I could accomplish some energy saving

the 2 pump scenario instead of a VFD is an option, (client already has pump and all equipment) I can suggest

I will try to explore the Arduino idea, I thought that having all he software Capabilities in the VFD, introducing another control element add more complexity

thank you all

Claudio

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#17
In reply to #16

Re: Help with VDF Pump Control

10/15/2014 10:12 PM

Using a good VFDyou don't need any special external controller as the firmware allows such basic functions.

If using a basic VFD you can can add a cheap PLC (starting at a few hundred US$ including a very small touch screen as HMI), just make sure it has the required analog and digital I/Os. For such crude regulation application you don't even need specific full-fledged PID functions, you can program everything yourself.

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