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Controlling a DC Fan with a Photohelic


Manville

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I have a Dwyer Series 3000 Photohelic and would like to control a 24volt fan. I am thinking I can use the high level and low level switches to control my voltage. I need a program that will slowly step up the current voltage if the low level is hit and slowly step down the current voltage if the high level is hit. I am extremely new to PLC programming and I have looked through the sample programs and still have no clue. :-) I have an M90-TA2-CAN controller. Any hits or ideas?

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  • MVP 2023

How exactly are you going to step the voltage and what are the steps? Have you determined in what voltage range the fan is effective (if you spin it too slowly, it will do nothing).

What you probably need to do is create a crude PWM (pulse width modulation) setup. The M90 does not have this function like the Vision series does, but you could make one. If you don't know what PWM is then do a little research on the Internet. It will give you some insight as to what your program needs to do.

Joe T.

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How exactly are you going to step the voltage and what are the steps? Have you determined in what voltage range the fan is effective (if you spin it too slowly, it will do nothing).

What you probably need to do is create a crude PWM (pulse width modulation) setup. The M90 does not have this function like the Vision series does, but you could make one. If you don't know what PWM is then do a little research on the Internet. It will give you some insight as to what your program needs to do.

Joe T.

My original thought was to have the PLC start up with a set voltage (let's say 7 volts) and delay 15 seconds to give the fan time to get up to speed and establish some pressure in my chamber. My photohelic will then switch based on it being too low or too high. I would use this switch to tell my program to now add or subtract 1 volt to my current output voltage. Once the fan is between the set point both switches will be open and nothing changes until my pressure drops or gains. I was hoping this could be done with a simple program. Maybe I am wrong.

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Hi Manville,

Do you have any fan driver or just fan with two wires?

What is a fan current?

To drive a fan voltage, you need additional driver, as an analog inputs and output of M90-TA2-CAN is 0-10V.

Analog output have 1Kohm minimum load impedance.

This means that the max current you can obtain theoretically at 10 V is 10 mA.

Seems far below the one you need to drive any kind of fan motor.

*Digital Output have current limit 0.5A, but you need realise PWM, as Joe say.

Be more specific with your specifications, then answers will be fastest and more specific as well.

Best regards,

Alex.

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  • MVP 2023

Alex is exactly right- we need the specs to your fan to be more helpful. Just as a guess, I dug around for the specs on an 80 mm 12V computer fan. These draw about 170 mA, so there's no way you're going to connect something like this to an analog output if that's what you were hoping to do.

The M90 you're using has PNP outputs that are usually powered by 24V, but you may be able to power them with another voltage that matches the fan. This is a question for the creators.

A PWM program for the M90 would not be complicated. Instead of thinking in terms of control voltage, you will actually be quickly pulsing the fan with current which will work just as well. The feasibility of your hardware design needs to be resolved first. Have you asked your distributor for help?

Joe T.

Later in the evening....

I wanted to test my theory that it wouldn't be a complicated program so I put some code together. This would work in an M90 or a Jazz with transistor outputs. Of course the easiest way to get PWM is buy one of the units that has an HSO output.

M90 PWM.U90

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  • 4 months later...
  • MVP 2023

You can not access the SD card directly using data table functions. You could create logic to transfer data tables back and forth from the SD card and create a very large virtual data table. What exactly is your application? How many rows can you define with your current data schema?

Joe T.

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