Hi ALL, I need to control the temperature of a furnace. The Thermocouple ouputs are available as RS-485. What Hardware and system configuration should I prefer?

[Gurdas Singh]

I need to automate the control of a gas carburising furnace. The available signals are Thermocouple K-Type (4 nos., one each from the three zones and one from the geometrical center of the furnace) and Oxygen Analyser. That makes it a total of 5 signals, all available in RS-485 format, which I need to acquire (10 samples/second) and then initiate a control action as per the rule base. Reliability is a major issue and the system has to work in harsh conditions.
What hardware would suit my purpose? I would prefer NI hardware which can be programmed via VB or VC++. LabVIEW may be considered as the last option.
Apart
from using the thermocouple/Oxygen analyser signals for controlling it is also desired to store them on a PC for analyses and visualisation (via graphs etc etc)
My need is URGENT and would appreciate any help. Thanx in advance
Gurdas

[Greg Caesar]

Mr Singh,

We would really need one more key piece of information about your sensor. You mention that the thermocouple signals are available through the rs-485 format. To me, that must mean that you already have some type of device that converts the millivolt thermocouple readings to serial information that can be retrieved by a controller on a rs-485 bus. Or to be more specific, you must be using some sort of industrial hardware, such as a Remote Telemetry Unit or PLC to convert these thermocouple readings to rs-485. However, your industrial hardware should also specify some form of communication protocol that it uses over rs-485. This protocol is what describes the commands that are sent/received over the rs-485 bus to talk to your device, and this will therefor
e determine the interface software on the computer. For example, two common protocols used with rs-485 communication are Modbus and Optomux. Therefore, the computer would need software that could "speak" this protocol (such as Modbus or Optomux) over rs-485.

On www.ni.com, we have a KnowledgeBase titled "Drivers for Communicating to PLCs, RTUs, and Other Industrial Hardware" that provides an excellent overview of the software interface to VB, VC++, and LabVIEW for this type of industrial communication. Here is a link:

http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/13ee0a9e2c43f0db86256a6100722651?OpenDocument