Watlow Electric 988 用户手册
WATLOW Series 988 User’s Manual
2.5
Installation and Wiring, Chapter 2
Wiring
Sensor Installation Guidelines
Maintain isolation between input 1 and input 2 to prevent a ground loop.
A ground loop may cause incorrect readings, dashes across the upper dis-
play or the display of error codes.
A ground loop may cause incorrect readings, dashes across the upper dis-
play or the display of error codes.
Thermocouple input: Extension wire for thermocouples must be of the
same alloy as the thermocouple itself to limit errors.
same alloy as the thermocouple itself to limit errors.
Using grounded thermocouples for both input 1 and input 2 may create
ground loop problems. To correct this problem, replace at least one of the
grounded thermocouples with an ungrounded thermocouple. If the appli-
cation requires grounded thermocouples, use an isolated transmitter,
such as a Watlow Gordon 5702 isolated transmitter.
ground loop problems. To correct this problem, replace at least one of the
grounded thermocouples with an ungrounded thermocouple. If the appli-
cation requires grounded thermocouples, use an isolated transmitter,
such as a Watlow Gordon 5702 isolated transmitter.
RTD (100
Ω
) input: Each 1
Ω
of lead wire resistance can cause a +2°C
error when using a two-wire RTD. A three-wire RTD sensor overcomes this
problem. All three wires must have the same electrical resistance (i.e.,
same gauge, same length, multi-stranded or solid, same metal).
problem. All three wires must have the same electrical resistance (i.e.,
same gauge, same length, multi-stranded or solid, same metal).
Process input: Isolation must be maintained between input 1 and input
2. If both input 1 and input 2 are used as process inputs, a separate
power supply and transmitter must be used for each input. Output option
T (external signal conditioner power supply) can be used to supply power
for only one input.
2. If both input 1 and input 2 are used as process inputs, a separate
power supply and transmitter must be used for each input. Output option
T (external signal conditioner power supply) can be used to supply power
for only one input.
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CAUTION:
The Series 988 will
not function with
two grounded ther-
mocouple inputs.
Avoid using a
grounded thermo-
couple for both
input 1 and input 2.
Failure to follow this
guideline could
result in damage to
equipment.
The Series 988 will
not function with
two grounded ther-
mocouple inputs.
Avoid using a
grounded thermo-
couple for both
input 1 and input 2.
Failure to follow this
guideline could
result in damage to
equipment.
NOTE:
Input-to-output iso-
lation is defeated
when the external
signal conditioner
power supply is
used to power a
transmitter connect-
ed to input 1 or
input 2.
Input-to-output iso-
lation is defeated
when the external
signal conditioner
power supply is
used to power a
transmitter connect-
ed to input 1 or
input 2.