A simple programming question!

Shane1981

Member
Join Date
Oct 2005
Location
australia
Posts
1
Hello guys,
I am using GeFanuc Series 90 micro PLC and logicmaster 90 to program it. I want to know how would we program this in ladder diagram programming:
what rung or commands would actually read the analog input from a sensor which should be 0-20mA, compare it with a threshold value, if it'z greater than that, turn on a relay or a light at output, if it is below that, turn it off. Suppose analog input is connected to input number 1 and output is at output no 1. Thatz it!
Hope to get a quick reply. Any links to point in the right direction are welcome as well! Thx a lot guys,
Shane.
 
First of all, you have to connect your 0 - 20 mA signal to an analog input, not to a discrete input. If you don't have the version of the Series 90 Micro PLC that accepts analog inputs, then you're out of luck.

If you do have a PLC with analog capabilities, then you use one of the six relational instructions in the Series 90 function set. (GT, GE, LT, LE, EQ, or NE). Are you the same person as sss94 who asked the same question the other day?
 
Shane:
Steve is dead-on on his answer. Remember at its most basic level the micro proccesor only understands binary! You need an analog input that contains a analog to digital convertor.
This will convert the analog signal to a 16 bit word. Then you can manipulate that data into a register....
If the Micro you have doesn't have an analog input, you might want to try a GE Versa-max micro......
 
You could try this.

In the past I have configured the inputs on a GE Micro to be a high speed counter. Information on how to do this is available on the GE Web site. Then I have used an Analog to Frequency module from Calex, to convert the analog signal to a 0-500Hz frequency, which is counted by the configured input. You will need to do some scaling within the PLC, but this will work. Go to www.Calex.com for more information. I believe the module that you would require would be a 8605.

Good Luck.
 

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