Basic Electrical input PLC questions.

AmazingTrans

Member
Join Date
Nov 2005
Location
Illinois
Posts
38
Hello everybody,

I have a quick question about electrical knowledge. Right now I have a 5V DC sensor, and I want my L32E AB 24V DC input card to read the signal. Anybody any idea how can I do this? Is there any AB input card that read 5V only? Do I need to use Op Amp? Voltage regulator? Your ideas are very much appreciated. Thanks
 
If your sensor just sends OFF and ON information which you want read by a PLC, I would suggest you use a simple transistor. In addition what you would need is a 24V power supply....most probably, your PLC would have a continous 24V output supply which you could use. So, you connect the Output of the sensor (5V) to the Gate terminal of the transistor, you might need a resistor to limit the current. Connect the +24V and COM to the other two terminals depending if you use a NPN or a PNP. Also, the common would need to be shorted with the Common of the sensor.

This to me is the easiest option, you could alternatively use a realy but if the switching frequency of the switch is fast, a realy wont be able to keep up. Transisitors are high frequency devices and much cheaper so I guess it should be a good solution

Ohhh BTW.....make sure the transistor does indeed start conducting with a Vcb/Veb of 5V again depending on if you choose to use a NPN/PNP.
 
You could use a signal conditioner. There are many brands available Crydom and Gordos are two brands that come to mind quickly. That's a commercially available equivalent to breadboarding your own transistor interface.

You could wire the sensor to a small relay with a 5 volt coil and use a contact from the coil as an input to the PLC.

If this is on an actual production machine, the most reliable solution is to either change the sensor to match the PLC input module or change the PLC input module to match the sensor.
 
Some manufacturers still have TTL input cards available for the latest PLCs. However, the whole input card is TTL.
 
Contact your A-B distributor. If you give him exact info on the sensor he undoubtedly has the bits and pieces available to make this happen. I'm not sure you have provided enough info here for an exact solution.
 
Signal Conditioner

I've thought about getting the signal conditioner by Crydom. The SM series Output Module and the digital I/O Mounting board.
Yup, this is going to be used for roll calculation. I have a couple of sensors that is 5V voltage, and they are used to determine the speed of a web, the amount of roll left etc, and open close of a device.

Do you guys think will it be fast enough to track roll pulses. I have a 96 tooth roll gear that the sensor sense.

I got myself the SMODC5 since the input from the sensor is 5V and the output of this SM module I can put it to 24V so the input of the PLC can read it. Do you think it will work?

http://www.newark.com/NewarkWebCommerce/newark/en_US/endecaSearch/partDetail.jsp;jsessionid=FKEIFHKFAIBSYCXDUY2SFGIK2OTCIIV1?SKU=98F993&N=0
 
Opto-22 signal conditioners can also be used, on a dumb backplane. They also have some high speed ones.
Those are my choice for industry, as they have diagnostic LED's, and are easily replacable by the mantainance staff.
 
Since you are using your sensor for speed monitoring you might want to consider using a high speed counter module. This would accept your 5V signal without any conditioning and could make your code simpler and more accurate at high pulse rates.
 
Andybr is correct. You should use a high speed counter in this application for two reasons.

1. The high speed counter can accept the 5vdc.
2. You might miss pulses when counting the sprocket when using standard inputs.
 
I've used this module (5225)from PRelectronics before and it works great. You can power up the sensor and convert the output to a PNP/NPN transistor output. Speed is not an issue with this thing either, it has a max frequency input tolerance of 20,000Hz and the output is isolated from the input and supply.

http://www.prelectronics.com/idd1027.asp
 

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