A 593 unit lets a 751, 752, 751-SG or 851 unit measure thermocouple temperatures. It is an isothermal box which also provides screw terminals, allowing the signals to be permanently wired.
You plug the 593 into the data acquisition unit with a ribbon cable. It includes a cold junction sensing RTD (resistance temperature device) with an associated constant current source (0.8 milliamps). The RTD is used to determine the temperature at the termination point. This reference temperature is used with the analogue input channel's voltage reading to calculate the temperature at the thermocouple's junction.
The cold junction is automatically connected to the auxiliary channel on the data acquisition unit and compensated for in software. The channel is read directly showing the cold junction temperature in Celsius.
The software has built-in linearisation for B-, E-, J-, K-, N-, R-, S- and T-type thermocouples. All readings are saved in the engineering units of your choice: Celcius for example.
The unit also offers protection from high voltages when series resistors are fitted. Noise problems can be solved by fitting an input filter and broken thermocouple leads can be detected.
For an artice on how to measure temperature see Issue 5 of our Monitor newsletter on the Data Acquisition Intelligence site.