PLC and analog inputs.

kerimdira

Member
Join Date
Nov 2012
Location
malaysia
Posts
5
hello everybody.
MY plc is cpm1 20cdr-a(omron).
i m using this plc and i m facing problems related to:
1- i have moisture sensor(analog input) that on/off a valve(digital output)
so how can i do? is there thresholding inside plc so that it convert it automatically? or is there any way to threshold the analog input to make it digital using cx programmer?
2- my plc output capacity is 24vdc and 0.3A. i want to on/off two 12vdc valves and 12vdc pump(0.3A). i m thinking the plc output(24vdc) should be regulated to 12vdc. m i right?
or plc output can't on/off motor? if it cant then i need to use a relay switch.
3-a plc output come with only one wire and valve need to wire(+ and -) so is plc output wire has polarities?

any help will be appreciated.

best regard
 
1- i have moisture sensor(analog input) that on/off a valve(digital output)
so how can i do? is there thresholding inside plc so that it convert it automatically?
No it is not automatic, but must be programmed by the user (you). Set up logic in you PLC using comparison instructions: "If Moisture Input > (Greater Than) XX, turn on valve(digital output). If Moistuer Input < (Less Than) YY, turn off valve".
2- my plc output capacity is 24vdc and 0.3A. i want to on/off two 12vdc valves and 12vdc pump(0.3A). i m thinking the plc output(24vdc) should be regulated to 12vdc. Am I right?
No, not for a digital (on/off) output. You have to use a relay with a 24 VDC coil to control your 12 volt devices.
 
Last edited:
thanks man.

your explanations will help me too much.
regarding the analog input what you mean is just to find out the range of the analog sensor(moisture) for example (25) and instruction in plc programmer like (>) and converted in cx programmer?


l.............||.................(>)25.......o........|
 
Yes, read the analog signal, and scale its range, if needed, or use the raw input values. Then decide at what analog moisture values you want the digital on-off valve to open and close.
 
thanks for the help.
regarding the the output plc wire. from every output pin there is a wire need to be connected to a relay(+/-) it has polarities(+/-)?
 
from every output pin there is a wire need to be connected to a relay(+/-) it has polarities(+/-)?
Yes, I think your PLC is a "DC" model, which uses Direct Current voltage, so every device connection has a + and - terminal. Usually (-) is a "Common" terminal. If it is, then connect your device (-) to Common on your PLC or power supply.

For the Omron CPM1A-20CDR, the COM (-) terminals are the top row on the bottom (output) side of the unit, labeld "COM" with lines pointing to the terminal screws. All of your PLC Output terminals (bottom row) are then (+) polarity.
 
Last edited:
got a new obstacle: my computer doesnt have serial port so i bought a USB converter. i install the CD for usb converter and i checked the number com(4) from the device manager and i direct my cx programmer with the same number of com(4) also i select the correct device name(cpm1). when i tried to connect it says:plc failed to connect. and ask me to check
1the device selected in cx programmer
2-the network setting of change plc dialog
3-the power supply to the plc
4 the connection between plc and pc

of course the power supply is connected as well as the connection between plc and pc.

any help
 
Cheep converters are a waste of time. I use the Omron - not cheap but works.
 
What cable/interface are you using to connect to the CPM1?
The Omron serial cable is NOT a standard pinout.
BobB is correct about USB/Serial converters! Lots of post on this forum regarding these devices.
 

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