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Wireless Remote Pressure Gauge / Sensor

02/13/2019 2:58 PM

I'm designing a wireless remote pressure gauge to be installed at the end of a Valley irrigation pivot. Gauges like this typically output an analog 0 - 10 volts, but could vary a bit (powering the pressure gauge and RF (or other) transmitter can be solved a bit later). The transmitter would send this value to the well-house where the voltage would be reproduced and sent into a variable frequency drive (VFD) as an analog feedback signal which would control the speed of a booster pump...When pressure drops below a minimum level, the VFD would ramp up the speed of the booster pump to raise water pressure to an acceptable range.

The RF transmission distance is a max of 1,000 meters and can be line-of-sight if antenna at well house is raised on a pole.

I see some receivers out there that have relay outputs, but haven't been able to identify any with analog...Maybe remote control airplane technology might lend itself here...?...(thinking throttle control circuit, possibly)...

Any ideas to would be much appreciated.

Background: The pivot is not on flat ground. As it traverses, it does not need the extra pressure the booster pump provides until it starts climbing a hill. The hill is mild for some of the pivot's travel, but then gets steeper. I'd like to utilize the full capability of the VFD so that it can ramp up the pump a little on the lower hill, but then more on the steeper section (thus the analog feedback). This would also save a significant amount of energy vs. just turning the booster pump fully on when pressure initially drops below a certain threshold.

Thanks very much, -->Bob (farmer, rancher & electrical engineer)

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#1

Re: Wireless Remote pressure gauge / sensor

02/13/2019 3:04 PM

Enter the words “radio telemetry equipment” into an internet search engine, and go from there.

Don’t be surprised if the input/output connections are 4-20mA and not voltage, as current is a more reliable method of transmission than voltage.

In order to carry out control, a 3-term controller is needed, which may be already on-board; if it isn’t then it will need to be installed in addition to the equipment already selected and that indicated above. The process of tuning the controller is a combination of training and experience.

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#2

Re: Wireless Remote Pressure Gauge / Sensor

02/14/2019 1:41 AM

Hi Bob

If you search under Wireless I/O you will find what you need.

I set up a control system to cover dams, pumps, tailings ponds and settling dams to recycle water in a mine using Wireless I/O but as it was a large system it interfaced with PLCs over several kilometers and hundreds of metre height changes.

For your system a simple one hop unit would suffice and there are many that have analog I/O. Might I suggest 4 to 20ma analog terminated to 250 ohm resistor giving 1 to 5 volts. If using an 0 to 10 volt signal, there is no way to differentiate 0V from a broken wire for the 0V is still valid unless some form of broken wire monitoring is employed.

As for pressure measurements then use a pressure transducer inserted into a tapping point on the delivery pipe at the best location, usually the end of the line. Again these can be found with various sensing membranes, stainless, ceramic depending on the quality of the water and undissolved solids in the water. They require usually 24 volt DC and can out put my old favourite 4 to 20mA. Solar panels and a battery back up will provide the 24v and the load requirements are small. If you want to measure the pressure a meter can be hooked into or across the analog signal. Small digital displays cost almost nothing and you can plug them into where ever your fancy takes you.

One thing to be aware of is that the radio transmitted signal lies within the approved bands for the type of transmissions allowed by your regulator. It can be easy to buy a non complying radio system in a band and get yourself into all sorts of bother so specify that it must comply with the regulations of whom ever is your licencing branch.

Good luck with you center pivot. Here in Qld they are springing up all over the country side like crop circles.

Regards Stef

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#3

Re: Wireless Remote Pressure Gauge / Sensor

02/14/2019 8:35 AM

Banner, Balluff, WIKA, IMF Effector, Hycon

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#4

Re: Wireless Remote Pressure Gauge / Sensor

02/14/2019 11:08 AM

Depending on the RF frequency used, you may need to put the transmitter antenna on a pole at the swivel, to get the signal above the water spray. We happen to be having a major rain shower at the moment, and have no cell service as a result...

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#5

Re: Wireless Remote Pressure Gauge / Sensor

02/14/2019 12:16 PM

All- Thanks VERY much for all your thoughtful input. This might take me a bit to look into all your suggestions, but I will get back to you! A friend suggested another solution to arrive at the same result: install a flow rate meter in the irrigation pipe leaving the well house and hard wire its output into the VFD. As the flow lessens (due to the pivot climbing up the hill), the VFD would crank up the pump motor to keep the water flowing to all sprinkler nozzles and the end impact sprinkler gun. I think finding an inexpensive flow rate meter will be key. Much more fun to play with the wireless solution however ;-). Thanks again!

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#6

Re: Wireless Remote Pressure Gauge / Sensor

02/14/2019 2:51 PM

Does the location where the pressure is sensed have power to power the pressure transmitter?

If not, you need to be looking for a pressure sensor/transmitter with extremely low power consumption, probably with a DC voltage output, when battery power is needed.

Powering a 4-20mA signal continuously kills batteries in a (relative) hurry. Voltage outputs can be less power draining, but need to be designed as such, and that's not a high priority outside of the truly wireless market.

I carry a pack of three (transistor) 9V batteries wired in series to power-up 4-20mA transmitters in the field when DC power is in question. That battery pack, new, will run a 4-20mA two wire transmitter for 3-4 days, continuously 24-7.

The "truly wireless" market powers the sensor element with the same battery that powers the radio. But that's Wireless HART and ISA 100 technologies designed for the process industries, either of which has a $6-$10K start-up cost.

Banner has a special model battery powered radio that can be configured to power an external device, but when used on 4-20mA level transmitters the radio battery can power the device 2-3 times per HOUR for a 6 month battery lifespan, not exactly the update rate you need for pumping water. Even a Banner node (field) radio and a gateway (other end) is an $800-$1000 proposition.

Rosemount has a low-power gauge pressure transmitter with a voltage output designed for remote useage on pipelines and oil/gas fields, but again, it's $2-2.5k device.

Most industrial use assumes that power is available, so transmitters are not designed for ultra low power consumption.

Look at Great Plains (Flomec) for plastic flowmeters for water.

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#7
In reply to #6

Re: Wireless Remote Pressure Gauge / Sensor

02/14/2019 5:31 PM

Those prices are precisely why OP was asking about using a hobby type remote control!

I do understand that they are low-volume products, so have a high development cost per unit sold, but several k$ each is exhorbitant!

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#8
In reply to #6

Re: Wireless Remote Pressure Gauge / Sensor

02/15/2019 1:44 AM

There might be power out there near the end of the pivot...I’ll need to check. If nothing else, I could wire in a step-down transformer off one of the phases of the 3 phase power that runs to the wheels of the last tower. Then a small “brick” power supply could do the rest.

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#9
In reply to #5

Re: Wireless Remote Pressure Gauge / Sensor

02/15/2019 2:02 AM

Did a bit of work on this today. Turns out that IMF Effector has a relatively inexpensive flow probe (Under $400USD, no moving parts, digital, analog & IO-Bus outputs). It’s their AS series. I think it might work even though it’s not exceptionally accurate. All I need is relative flow changes...More research to do (of course). All your comments are greatly appreciated!

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#10
In reply to #9

Re: Wireless Remote Pressure Gauge / Sensor

02/15/2019 7:40 AM

Check out SCADA systems used by lots of utilities and industries.

No need to reinvent the wheel.

You can monitor and control just about anything with this system.

I only linked to one brand,but shop around,there is much competition in the field.

https://www.emerson.com/en-us/automation/control-and-safety-systems/scada-systems

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#11
In reply to #9

Re: Wireless Remote Pressure Gauge / Sensor

02/15/2019 4:15 PM

Phoenix Contact also has a robust line of wireless io with one install I know of over a decade old with only interruptions due to poor grounding and lightning, in middle Georgia.

https://www.phoenixcontact.com/online/portal/us?1dmy&urile=wcm:path:/usen/web/main/products/subcategory_pages/Wireless_IO_P-08-11-03/a551dde8-eef5-4227-9401-1e1f9718e2b8

The flow meter is a better idea, you can characterize your pump speed reference input or flow controller output to be square root, which then linearizes your pump speed to flow, i.e. a 10% flow increase demand is met with a 10% PID controller output

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#12
In reply to #5

Re: Wireless Remote Pressure Gauge / Sensor

02/16/2019 5:00 AM

Hi

I have been thinking on your problem and as Pirot would say the grey matter she is active. To measure flow but not necessarily a quantitative value but a fall in flow might I suggest using DP differential Flow across an orifice plate or a venturi to arrive at a value to start the booster pump.

The orifice plate could be just a restriction in the form of a plate with a smaller orifice in the line to the travelling irrigator. As for a venturi there are certain upstream tapers and downstream tapers needed for the proper DP to be generated but I have seen a crude venturi made from a tapered adapter like 8 inch line to 6 inch line a small 6 inch nipple then a 6 inch to 8 inch long taper adapter, crude but it worked.

If you only want to sense the drop in flow then a differential pressure switch connected from the upstream portion of the adapter to the neck or across the orifice plate should give you a switch point such that you can start the booster pump to help with the hill climb. DP switches are a cheap alternative to the more advanced method of measuring exact pressures and doing the maths in a controller.

Regards Stef

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dkwarner (2); Don Blashka (1); HiTekRedNek (1); Iris (1); PWSlack (1); ranch engineer (3); rwilliams (1); Stef (2)

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