West Control Solutions KS 816 - Manual (Page 12)

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Multiple transmitter and temperature controller KS 816
The controller inputs are not galvanically isolated. Therefore, thermocouple measu-
rements above approx. 700°C and unsuitable thermocouples imply a risk of measu-
rement errors.
This effect is due to the fact that the isolation value between protective tube and
thermocouple, dependent of construction type and insulation material, decreases to
values of some kOhm from these values. Additionally, ionization of hot gases can
cause potential differences between the thermocouples, which can cause measu-
rement errors or trouble due to compensating currents.
For the same reason, there may be problems when using mixed grounded and in-
sulated thermocouples.
The max. permissible potential difference between thermocouples is 7V
pp
.
We urgently recommend to avoid using mixed thermocouples.
If using grounded and insulated thermocouples in an installation should be
unavoidable due to other reasons, the negative arm of the insulated ther-
mocouple must be grounded at KS 816.
Already grounded thermocouples must not be grounded for a second time!
When replacing insulated thermocoupl es by non-insulated ones, removing
the ground connection of the negative arm at KS 816 is indispensable.
5.1.1 Cold junction temperature compensation
The four possibilities of temperature compensation are:
1. The temperature compensation is ineffective (for PT 100- or U/I inputs)
2. Internal temperature compensation. Compensating lead is used up to the
KS 816.
3. External temperature compensation. Compensating lead is used only up to the
cold junction reference, the lead between reference and KS 816 can be of copper
4. Cold junction reference remote measurement. Input IN16 can be configured so
that it operates as input of the temperature sensor of a remote cold junction refe-
rence.
The thermocouples of the individual channels are taken up to a common reference
by means of compensating leads. The lead between reference and KS 816 can be
of copper. The 16
th input is used for measuring the reference temperature and for
correcting the input voltage accordingly. Because of the measuring accuracy, the
sensor should be a resistance thermometer. When using this temperature compen-
sation method in an installation with several KS 816 units, this method mut be used
for each individual unit.