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K8AC-H

Voltage Fluctuation Compensation

The voltage fluctuation compensation function automatically adjusts
the burnout alarm value of the K8AC-H according to voltage
fluctuations in the heater circuit.
The operating value for burnout detection when multiple heaters are
connected is set very close to the normal value. Thus, a false burnout
alarm output will occur if there is a voltage drop in the heater circuit.
The voltage fluctuation compensation function prevents this type of
false output.
Example: Voltage Drop from 100 V to 95 V in the Heater Circuit

Conditions:
Voltage fluctuation compensation standard value = 100 V
Burnout alarm set value = 10.0 A
If the power supply voltage drops from 100% to 95%, the
operating value will also reduced from 100% to 95%.
Burnout alarm operating value = 10.0 A

95% = 9.5 A

Gate Input

The gate input provides a sync signal used to link burnout detection
to the control output of the temperature controller.
For SSR control, the voltage output pulse from the temperature
controller is input.
For ON/OFF control, 24 VDC linked to a relay contact of the
temperature controller is input.
For cyclic or phase control, a 4 to 20-mA control signal is input.
If there is no gate input for a Heater Element Burnout Detector, a
heater burnout alarm would be falsely output when the voltage output
pulse from the temperature controller turns OFF, and there would be
no way to tell whether it was a false output.
Note: The gate input function can be disabled. If it is disabled, Heater

Element Burnout Detector operation will not be linked to the
temperature controller control signal. (The gate input can be
used as a simple undercurrent relay.)

Power-saving Operation

If there are no key operations performed within a preset time period,
the display automatically turns OFF.

Output Operation Time Charts
Heater Burnout and Heater Layer Short Circuit
(Overcurrent) Alarms

SSR Short/Open Circuit Alarm

Using the Power Regulator's Gradient Settings

The power regulator's gradient settings can be used to prevent
malfunction by setting the operation gate current level. The
relationship between the gradient settings and output current
depends on the power regulator manufacturer and model, so be sure
to check the characteristics of the power regulator being used before
setting.

Setting Example
Initial setting: 7 mA

When the power regulator's gradient settings are changed, the
operation gate current level is set so that the output current is within
the measurement range. (In the following diagram, 14 mA is set.)

Using Halogen or Other Heaters with Varying
Resistance during Phase and Cyclic Control

When phase control is used with halogen heaters or other pure metal
heaters, the heater resistance fluctuates according to the control
level. As a result, high-precision detection of heater burnout is not
possible. The effect on the heater and setting methods depends on
the heater being used. Therefore, consult with your OMRON
representative before using a heater with varying resistance values.

Halogen Heater Resistance Fluctuation Example
In the following example, burnout of one element in a six-element
heater can be detected at a control level of 20 mA, but detection is not
possible due to the effect of fluctuating resistance if the control level
is any lower.

Power Save Mode
Standby Time

Heater burnout set value

Heater current

Alarm hysteresis

Heater layer short circuits

Overcurrent set value

ALM indicator lights. ALM indicator lights.

Alarm output

SSR open-circuit

SSR indicator lights. SSR indicator lights.

Alarm output

SSR short-circuit