Pretty new to PLC programming.

This is my first smaller project im designing a hot water control PLC, the tank is 50k gallons and can release water from two points within the tank, one point is at the bottom and another point is around the middle of the tank. This is because the hot city water enters in at the top of the tank making the hot water at the top of the tank, there is a level sensor and a temp sensor at the bottom of the tank so we know the temp and fill,
The water can be released at another point of the bottom of the tank so it can be heated by passing through a heat exchanger and then reentering at the top of the tank, but the water has to flow through a pump before reaching the heat exchanger, I need to control the speed of the pump using a powerflex 532 VFD I am using rslogix 500 for this project but i have this point and have gotten stumped, what logic do i use to control the speed of a vfd?

meggettc said:

This is my first smaller project im designing a hot water control PLC, the tank is 50k gallons

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Anything but small...

meggettc said:

i have this point and have gotten stumped, what logic do i use to control the speed of a vfd?

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What is your pump doing? , feed supply, feeding another process, heating the water, maintaining level?

Are you trying to target a temperature coming out of the heat exchanger using pumps speed rather than a proportional valve on the steam line?

Why use a VFD? Power savings maybe? Are you afraid of temperature rise in the heat exchanger(s)? I love VFDs but simple ON/OFF systems work much better when your maintenance department is full of idiots.