cFP- 2xxx controlling multi low voltage devies spread around 10m apart CANBUS? RS485?

[Monkins]

Dear all

Currently we use a cFP-2100 that conrtols relays and uses a voltage input card to read the results from a microwave measurment device in a box.  This system is inside a cabinet and the fieldpoint connects to the microwave box and controls it with the RS232 port.

What we want to do is expand this system from a single node to a multiple node system possible up to 32 nodes of microwave boxes all transmitting the data back to the cFP. These nodes will be spread around a noisey industrial environment. 

My first thoughts would be to change the RS232 to a CANBUS or RS485.  Then link all the boxes along a bus.

The controller in the microwave box is easily changed to a CANBUS or RS485. and is powered by 24Vdc.  Also the devices will be about 10m away from each other in a long daisy chain.

We also have a cfp_2120 that has RS485 on it, i thought maybe this could be used to link up all the devices.  But i'd prefere to use canbus.

Whats the best way to connect a cFP to a canbus and if this cannot be done, whats the best alternative.

All thoughts ideas are appriciated

Many thanks, Chris.

[Ian Colman]

Hi Chris,

It would not be possible for you to directly network your cFP system using CAN unfortunately. Obviously RS-232 would not be noise resistant enough for your application but I would recommend considering RS-485. RS-485 is resistant to noise due to the differential nature of its communication. It also allows you connect multiple devices together as you desire and you would need to change your national instruments hardware.

Once you have considered this please let me know your thoughts.

http://digital.ni.com/public.nsf/allkb/2CABB3FD5CAF2F8686256F1D005AD0CD

Kind Regards,

Ian
Applications Engineer

National Instruments

[Monkins]

Ian Having looked at differnt RS485 interface chips like the MAX485, I see on long networks you need to install a resistor on the first and last node on the bus.  This would be simple on the circuit boards but for the compact filed point would there have to be a little board made up?  The total length of the bus would be about 500m and number of nodes 16. Could I get away with out the resitors?

Many thanks

Chris

[Ian Colman]

Hi Chris,

Yes you will need the resistors at the end of your daisy-chain. This is how the bus recognises the end of the network. If you could let me know how you are getting on and your thoughts on this, that would be great.

Ian