Need to connect 60 pressure sensors to a PLC

dbaid

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Join Date
Apr 2015
Location
Bangalore
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Hi all,
I am new to PLC's and need to connect 60 pressure sensors to a PLC.
Also the data from the sensors needs to be sent to a central location so the PLC needs to be connected to a cellular connection and also a GPS module.
Can any one suggest a solution.
Also how will I have to power the sensors or does the PLC power the sensors.

Thankyou.
 
Personally, I would consider an ASi bus system, this is a two wire, addressed system where the same two wires supply the sensors as well as take info from them. Have a look at GOOGLE, there are many automation companies that manufacture such systems with a lot of information on their implementation.

Steve
 
Unless you need the PLC to do some other functions, you're overbuying.

There are multichannel analog I/O modules that convert the analog pressure to Modbus, for example. When you have to ship the data out wirelessly it ends up being in some digital protocol, so why not convert to the protocol immediately?

I know Acromag has multichannel I/O, Opto 22 probably does, and there must be dozens of other vendors.

Industrial pressure transmitters are typically two wire 4-20mA, sometimes 3 wire 1-5Vdc. Either requires a DC power supply, typically 24Vdc. There's 33% less wiring with 2 wire than 3 wire. You need AC power to power the DC power supply. I NEVER use the PLC power supply to power the field devices. I ALWAYS use a separate, stand-alone DC power supply. The better DC power supplies can be paralleled for redundant performance.
 
Thank you very much Danw,Nehpets.

Can u elaborate a little on the ASI bus and;

what does "The better DC power supplies can be paralleled for redundant performance." mean

Mine are two wire sensors.

What PLC's can I use?
 
If you have one power supply, and it dies, then your whole system being powered off it dies. The basic models can not be wired together... the better ones can, which means if one dies, the 2nd one keeps the show going. This is known as redundancy.
 
You need an analog input for each of the pressure transmitters.

You need to go wireless. There are lots of wireless radios that handle Modbus.

This I/O box handles 64 single ended 4-20mA channels for about $50/channel and you end up with all the data in Modbus registers on an ethernet port. It's a Modbus/TCP slave/server. The radio will have to be a Modbus/TCP master/client. It's not a PCL, but this task does not call for a PLC, it calls for I/O and wireless.

http://www.acromag.com/catalog/305/...bus_I_O/Ethernet_I_OModules/Analog_I_O/ES2163

Single ended inputs will probably work if the pressure transmitters are 2 wire loop powered (which they probably are) because those are usually isolated from ground. Use the same DC power supply for all the transmitters (2 amp).

Here's a link to a redundant module used between 2 redundant power supplies.
https://www.phoenixcontact.com/onli..._p-22-02/4f8b0416-f42c-4ed2-b1f4-492fa9bd89bb
 
Before you go too far down a path of deciding on a technology or a vendor up front, you need to establish your needs in a clearly defined manner. I'm not going to do it all for you, but here are some examples of why this is important. maybe others can contribute their thoughts to the list.

  1. Resolution: How accurate does the measurement need to be?
  2. Noise immunity: How much resolution are you willing to sacrifice in order to filter out erroneous signal noise up front before sending it on somewhere else?
  3. Sampling Speed: How fast and how often does the AI need to sample the analog values?
  4. Data Speed: How often and how fast do you need to read the data at the other end?
  5. Multiplexing: Depending on the data speed answer, can you use multiplexing to concentrate your signal transmissions so they can share communication channels?
  6. Environmental conditions: How rugged do the field devices need to be in terms of ambient temperature, degrees of pollution, vibration etc.?
All of these issues are important because depending on your answers, some technologies or vendors will be unqualified from the outset and you don't want to waste your time with those.


Use your H.E.A.D: Have a plan, Execute the plan, Acquire the right technology, Do it once.
 
What sensors are to be used?
if 4-20 mA you will need a lot of input cards, or make a soultion with a 1-10 Volt card and a relais system.
look into Arduino for this a easier solution and a lot cheaper.
 
Thanks danw,

We cannot use the ethernet technology need to use a GSM based system.

just because you are sing gsm doesnt mean you cant use ethernet. virtually every cell modem now has an ethernet port. you would just port forward from the wan side of the modem to the local ip address of the modbus tcp module, usually port 502.
 

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