You need a Microlink 593 unit when monitoring thermocouples with a Microlink 851 Ethernet device, a Microlink 751 USB device or a Microlink 752 resistance measurement unit. It is an isothermal box which also provides screw terminals, allowing the signals to be permanently wired.
The box sits next to the PC or Microlink, and 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 Microlink and compensated for in software. The channel is read directly showing the cold junction temperature in Celsius. The software does all the work for you: performing the linearisation calculations and converting, if necessary, the thermocouple readings from Celsius to, say, Fahrenheit.
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.