new for plc

hi,
I am new for plc. i have nais plc. i want do program with 4-20ma uv sensor.sensor connect with uv monitor and that monitor have 4-20ma digital output.monitor measure uv lamp intensity in %.
i want to do if uv lamp intensity go below 70% alaram is ON.
I want to know connection between monitor and plc. and which instruction i will use for this program.
if anybody know please give me reply.

lots of thanks,

patel

Have you any datasheet for that UV-monitor and what type of PLC you have ?

Patel, you may be making this harder than it really is. PLCs aren't magic. They follow the same fundamental electrial principles as any other device. You hook them up to your field devices just like you would any other indicator.

Wire the 4-20 mA signal so the current coming from the UV sensor teh way you would wire an indicator. Assuming the UV meter is loop powered the + side of hte power supply goes to the + of the UV meter. The - side of the UV meter (output current) goes to the + input on the PLC. The minus side of your PLC analog input goes to the - side of the power supply.

Inside the program, you use a compare function. If the analog input data is less than (<) 70% of full scale, turn on a discrete output. If you have a 12 bit input the range of data is 0 to 4095 and 70% is 2867.

The output is just a switch. When the compare is true, the output will turn on the light.

As Tom mentionned, your program will be likely very short. Give details on 1) your NAIS PLC and expansion(s) type(s) - for instance FP0-C14RS and FP0-A21, 2) your programming tool.

Depending on your PLC type and configuration, analog values are read at special addresses or in shared memory.

Your first goal : try to think, describe and explain your project on some basic manner. Don't use PLC related words. Don't forget any steps nor informations : how does your process start ? What or who resets your alarm... and so on !

Regards

Laurent