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Deadband
Open
High Limit
Process
Variable
Low Limit
Setpoint
Reset
Closed
50 C
20 C
Deadband
Closed
Reset
Setpoint
Open
Temperature switch and
controller testing in the field
Temperature switches and controllers are
commonly used in small processes and in control
loops where a programmable logic controller
(PLC) or larger distributed control system (DCS)
are not warranted.
Temperature controllers provide both switching
capability based on rising and dropping
temperatures, as well as a local indication of the
measured temperature.
Most temperature controllers have some form of
tuning, using damping and PID (Proportional,
Integral and Derivative values) for smoothing out
the measured process temperature,
reducing variability.
The terminology around switches can be
confusing. The set state of the switch is the
action the switch takes when an input stimulus
above or below a specified value is applied. This
stimulus can prompt an action such as closing
a switch, which in turn starts or stops a motor,
or opens and closes a valve. The reset point
is considered the relaxed state of the switch,
which is typically referred to as “Normally Open”
or “Normally Closed.” This describes the default
condition of the switch. Lastly, deadband is the
band of temperature equal to the difference
between the temperatures where a switch sets,
and resets. See illustration at left.
7526A
Precision Process
Calibrator
See pg 5
726 Precision
Multifunction
Process
Calibrator
See pg 6
754
Documenting
Process
Calibrator
See pg 5
714B
Thermocouple
Temperature
Calibrator
See pg 17
712B RTD
Temperature
Calibrator
See pg 17
Suggested test tools
54
Temperature Applications