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CAUTION: Do not apply any type of voltage to the display hold termi
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nals. Applying a voltage to the terminals may cause damage to the con
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troller.
6.4.1 Switch Status
Connect the thermal switch to the display hold terminals on the either the hot or
cold side. To enable the Switch Status while displaying the temperature, press
"UP" on the hot or cold side. The letter "o" (switch open) or "c" (switch
closed) appears to the left of the display and flashes when it changes states.
When the Switch Status is enabled, the displayed temperature does not show
the hundredth place or the units. (For example, if the switch is open and the
temperature is 25°C, "o 25.0" is displayed.) To disable the Switch Status,
press the "DOWN" key.
When the Switch Status is displayed, the Display Hold is also enabled, allow
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ing the operator to view the temperature at which the switch changed states and
the status of the thermal switch.
When the thermal switch changes states the controller does the following.
1. Displays the temperature at which the switch changed states.
2. Flashes the new switch status.
3. The controller continues in the above state until either the thermal switch
is returned to its original state or the set-point temperature changes.
Note: This feature is a useful to quickly monitor thermal switch state changes
with a rough idea of accuracy but is not accurate when compared with the dis-
played temperature. Enable Scan Hold (see Section 6.4.2, Scan Hold) to im-
prove the accuracy.
The following example demonstrates the use of Switch Status using the Display
Hold terminals.
Example 1
With the instrument displaying 25°C, set the set-point to 100°C and enable the
Switch Status by pressing "UP". When the thermal switch changes states at say
50°C, the displayed temperature shows 50°C and the status flashes "o or c",
while the block continues to 100°C. The display remains at the switched tem
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perature and "o or c" continues to flash until the switch changes status or a
new set-point is set.
6.4.2 Scan Hold
To enable scan hold, first enable Switch Status/Display Hold and the Scan Con
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trol (see Section 6.3.1, Scan Control)prior to setting the set-point temperature.
Scan Hold is similar to Switch Status/Display Hold but instead of displaying
the temperature at which the thermal switch changes status, it sets a new
set-point temperature to the current temperature at which the thermal switch
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6 Controller Operation
Temperature Display Hold