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13. Heater break alarm function
13-1. Heater break alarm function (current detection / alarm output function [optional])
The heater break alarm is a function whereby an alarm is given to let you know when the heater is broken. The function is effective for
preventing product defects and negative impact of insufficient power.
Note: Heater break alarm detection precision may be reduced if power supply voltage and output operation amount are modified as soon as
key sequence
‘
3-3 Hearter break judgement standard setting
’
is set.
13-1-1. Operation overview
In ordinary operating condition, measure the current of the steady heater by key sequence
‘
3-3. Heater break judgment standard setting
’
and use as
standard value.
Next input the current value reduction rate relative to the standard value (heater break alarm point) setting by key sequence
‘
1-12. Heater break alarm
current.
’
The heater break alarm determines heater break when the value is below the preset vale for at least 5 seconds and the alarm
is displayed on
the front display (status display). Control operation continues unchanged.
If alarm cannot be output because of unstable operation when booting, etc., you can disable HB alarm output by
‘
2-2. Di function selection.
’
When the alarm is output, it is canceled as soon as heater current recovers, and the
display in the front display (status display) is also canceled.
If self-hold is required, an external self-hold circuit must be constructed.
13-1-2. Setting method
1) Preparation before setting
Switch to
of key sequence
‘
3-3. Heater break judgment standard setting
’
of the manual operation screen (data change dot flashes).
Energize the heater near the actual condition of output for the device to sufficiently stabilize the temperature of the heater (load current at this time should
however be about 25% of the rated current).
2) Heater current value setting
When heater temperature stabilizes, press
and import the heater current value (standard value) (data change dot stops flashing).
3) Heater break alarm point setting (HB alarm trigger point setting)
Set current value for heater break within the range of 0
–
100% by key sequence
‘
1-12. Heater break alarm current
’
(alarm however is not triggered if
heater break alarm current is set to 0%).
Example 1: Detecting break for 1 of 5 heaters used
Current percentage for 1 break is 4/5 x 100 = 80%; set to about 90% between that and 100% current when operating normally.
Power supply
Heater
Heater rating
(per heater)
Voltage: 200 V
Current: 20 A
Power: 4 kW
Type: Nichrome
In the case of a heat source that uses a steady current of 100 A and five heaters with the same rating.
䕕
If you want an alarm to be given when 1 of 5 heaters is broken
0
䠂
20
䠂
40
䠂
60
䠂
80
䠂
100
䠂
90
䠂
Current value due to 1 heater being broken is 80% of the rating.
Taking disparity of heater resistance into account, we recommend setting to 50% increase of the
current value per heater in order to have the device operate reliably.
In this case, the current value per heater is 20% of the rating. Setting by 1 break
therefore would be current value per break (80%) + current value per heater (20%) x 0.5 = 90%.
100A
PAC18A
R
U
Example 2: If using 1 heater
Set to 50% between 0% current when broken and 100% when operating normally.
13-1-3. Precautions when setting
1) When setting standard current value of heater by key sequence
‘
3-3. Heater break judgment standard setting,
’
conduct output of the device at maximum
output within the output range for actual service conditions. If set outside the output range actually used or when output is small (load current is less
than 25% of the rated current), the impact of detection error could increase and result in malfunction.
2) Set heater break alarm point lower than usual by key sequence
‘
1-12. Heater break alarm current.
’
Depending on the type of load, detection precision may drop and result in malfunction.
Even in the case of constant resistance heaters, resistance value may vary according to heater temperature in some cases. In some cases, it may be difficult
to differentiate between that resistance value variation and resistance value variation due to 1 of several heaters being broken.
If there are many heaters (5 or more), if you set lower than the calculation value (value between 1 break and when normal), you may not be able
to detect break of 1 of several heaters, but this is effective for preventing malfunction of heater break alarms.
3)
A load with variable resistance (large temperature coefficient) can be controlled as an applicable heater, but the heater break may not be detected
correctly due to the large changes in resistance value against heat generation. When connecting a variable resistance load, the current value during
operation may be higher or lower than the steady heater current value measured in advance in the key sequence "3-3. Setting the heater break judgment
criteria". In such a case, it will be required to set a heater break alarm in consideration of the current change during operation to avoid false alarm.
Example: Using 2 heaters. If heater resistance is large when starting and current when starting is 70% of the heater current for ordinary operation, set
lower than 70% of the current when it drops. Because current when starting is 70% and 50% when 1 heater is broken, if you set to 60% between the
two, you can detect break 1 of 2 heaters in most cases.
4) In the case of light loads of less than 15% of the rated heater current, heater break may not be able to be detected.
With transformer loads, current detection precision may drop.
If using with light load (less than 30% of rated load) or transformer load to prevent malfunction, use 50% for the heater break alarm point setting of key
sequence
‘
1-12. Heater break alarm current
’
as the standard.
5) In order to prevent malfunction, the heater break alarm will not be triggered if output phase angle is less than 15%.
