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Function Block set up for temperature dependable extraction fans

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Hey everyone

I'm very much new to both ladder logic and plc controllers and am running U90. I'm trying to use a plc to control extraction fans as the output and a temperature probe to read air temperature. Trying to get the intake and out take fans to switch on when the temperature gets above a certain point, and then run until the temp reaches a lower point. I know that function blocks are required to do this, but are unsure of how to program the plc to read the temp probe or how to program FB's.

This may seem backwards compared to the calibre of the other posts here, but any help would be outstanding!

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In the hardware configuration of U90 select the model you are using that is capable of using temperature measurement. The M91 and Jazz each have three models. In the hardware configuration select the appropriate Analog Input capable of temperature measurement and select the type from the drop down menu. Then select an MI operand to link the value for the temperature. You can select either Celsius or Farenheight in the mode drop down menu.

I have written a simple example program that selects the analog input MI and compares it to a constant value. Using the comparison function blocks you can set the output to run. Another comparison block resets the output allowing the program to shut the output off at a value lower than the conditions that enabled it to run.


I would also recommend watching the Unitronics Webinar on the Jazz which describes how to create a basic program and goes over the software features.

Jazz Webinar: http://www.unitronics.com/Content.aspx?page=Jazz_program_in_U90

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The Vision 290 uses VisiLogic software, which is different than U90. U90 is only for the M91 and Jazz series controllers. You will need to download VisiLogic 9.5.0 from our downloads page. Then you will be able to use the Vision 290. It does not have built in I/O so you will need to use one of the snap in or expansion modules that has temperature inputs.

The logic that you use will be much the same as you saw in U90, setting them in the hardware and using compare function blocks to set the output.

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