Control.com - Nerds in Control

Right now, there are a number of sensors (mainly thermocouples and RTDs) connected from the machine to the panel. This means a lot of wires from the machine to the panel.

A way of reducing this wiring is to multiplex these sensors at the source (i.e near the machine) and transmit the data over a 4-20ma current loop. But then, an identifier for each sensor will also have to be added/superimposed on the current value.

HART protocol does exactly this. But is there another way of doing this? Any ideas? Thanks.

You could use remote I/O over ethernet or some other two wire protocol.
Give us some more detail on the system you are connecting to.

Regards,
Roy

The sensors are right now connected to a regular controller, where in the multiplexing and controlling action takes place. But this is open to modification, such that the wiring from the machine to the panel is reduced.

Are you referring to extrusion machines? Is it possible to have more information on the same?

Jari
iconcnl at vsnl. net

The panel is right now on an extrusion machine. However, this can be used in a variety of applications. Sending more information through email.

There are a couple of multiplexer systems that exist that will take a number of temp signals at one end and then reconvert back to separate analogue signals at the far end (Moore Industries is one), but also check to see whether the receiving instrument has a serial data input so as to avoid the reconversion process.

Steve
www.mtl-inst.com

Do you need to use HART protocol? Can you use Modbus RTU, Ethernet
Modbus TCP/IP, Ethernet IP, Profibus DP or other protocols?

We have multiplexed 16 RTD signal over one 4-20 mA signal along with two digital signals indicating change of channel and last channel respectively. The receiver needs to read the 4-20 mA signal and 2 DIs. This is all that is needed. System is in service at one of India's top pharma companies.

VK Aggarwal

vkaggarwal2 at yahoo dot com

By DIs, you mean digital inputs? Was the channel information sent separately, or over the 4-20ma line itself?