Elcon HiD 2000 Series, User Instruction Manual

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5-17
5.9 HiD 2061/2062
Functional description
Accepts thermocouple or mV input signals from a Hazardous Area and converts them to an isolated analogue
current signal in the Safe Area.
Input type, range and error handling parameters are configurable by switches and trimmers.
Outputs are isolated from input and referenced to the power supply common.
Model 2061 Model 2062
Application Guidelines
For thermocouple input, connecting wires must be of the same type of metal as the thermocouple or compensating
cable. In so doing, no thermoelectric junction will be present, thus creating stray signals as a function of the cable
temperature. Obviously it is important not to interchange the compensated cable conductors.
Since they are made of dissimilar metals, they would produce spurious thermoelectric junction with consequent
drifts in the measurements. In case of doubt on the thermoelectric emission polarity, you can use a magnet to
distinguish iron from constantan or nickel from nichrome. A simple polarity detection method, applicable to all
types of thermocouple metals, consists in creating a thermoelectric junction with the unknown wires (just twist
together the two exposed conductors) and heat with a match while observing the thermoelectric emission and its
polarity with a millivoltmeter at the other cable end. Note that the first metal named in each thermocouple pair is
always the positive (i.e. Iron-Const = Iron +, Const -)
For thermocouple input, a reference junction compensator is necessary near to the input terminals (Hazardous
Area side terminals 4-8 for channel 1 and 3-6 for channel 2) and its value must be Cu 109
Ω
, 0.1% precision
resistor.
For a proper ambient temperature compensation it is recommended to maintain a stable temperature on the
Hazardous Area terminals. The better temperature compensation condition is with horizontally positioned
termination board with the Hazardous Area terminals on the bottom side. The worst temperature compensation
condition is with horizontally positioned termination board with the Hazardous Area terminal on the top side.
The average temperature compensation condition is with vertically positioned Termination board.
In all case is important to avoid direct air flow on Hazardous Area terminals. Furthermore is recommended to
avoid high dissipation barrier near the compensator terminal.