RKC INSTRUMENT THV-1 - Heater Break Alarm Functionality; Alarm Delay and Type 1 Settings; Alarm Activation Conditions; Heater Monitoring Application Example

IMR01M01-E16
20
7.9 Heater Break Alarm Function
The Heater break alarm monitors the current flowing through the load by a dedicated current transformer (CT).
The THV compares the measured value with the set values, and detects a fault in the heating or cooling circuit. In addition,
there are several types of Heater break alarms depending on control methods and applications of these Heater break alarms.
Read this chapter carefully to choose an suitable method and set an appropriate set value.
7.9.1 Common function for all types
 Number of alarm delay times
To prevent producing a false alarm, the alarm function waits to produce an alarm status until the measured current by the CT
is in an alarm range for the preset number of consecutive sampling cycles. The parameter of the Number of alarm delay times
is to change the number of consecutive sampling cycles by 5-cycle increment.
Heater break alarm 1: (5 cycles) × (Number of alarm delay times)
Heater break alarm 2: (5 cycles) × (Number of alarm delay times) × 10
7.9.2 Heater break alarm for Phase control
There are two alarm types (type 1 or type 2) available for Phase control.
(1) Type 1
Type 1 can be used as follows by using two Heater break alarm set values. (Refer to  Application)
Heater break alarm 1 set value: The alarm can be output when a heater break occurs by setting the Heater break alarm set value.
Heater break alarm 2 set value: This alarm set value can be used as an auxiliary alarm. For example, it can be used as a
Heater deterioration alarm if set to any value slightly smaller than the Heater break alarm set
value to output the alarm before a heater break occurs when the load current decreases due
to heater deterioration, etc.
• The Heater break alarm of Type 1 cannot be used for heat generation substances such as noble metals making
large resistance changes with temperature variations. In addition, it cannot be used for heat generation
substances such as silicon carbide making resistance changes with temperature variations and a lapse of time.
• Type 1 cannot be used for any power supply waveforms other than a sine waveform.
 How alarm is activated
• When heater current does not flow (Heater break, malfunction of the control device, etc.)
When the phase angle is equal to or more than 15% and the current transformer input value is equal to or less than the
Heater break alarm set value for the preset number of consecutive sampling cycles, an alarm status is produced.
However, in order to prevent malfunctioning, it is so designed that no Heater break alarm occurs at an phase
angle of less than 15 % (less than 15 % of maximum load current).
• When heater current can not be turned off (Thyristor break-down or permanent damage)
When the current transformer input value is equal to or greater than the Heater break alarm set value for the preset number
of consecutive sampling cycles, an alarm status is produced.
The alarm will be turned off when the current transformer input value goes in and stays at non-alarm range for five
consecutive cycles.
 Application (When Heater break alarm 1 is used for detecting any broken heater or Heater break alarm 2,
for detecting any deteriorated heater.)
Refer to the figure below for action by setting the set values for the following parameters:
• Maximum load current set value for alarm (P)*: 20 A • Heater break alarm 2 set value setting (F): 15 %
• Heater break alarm 1 set value setting (q): 20 % • Heater break alarm 2 used/unused (K): 1: Used
• Number of alarm delay times (r): 0 times • Alarm output state selection (c): 0: ON at alarm output
• Heater break alarm type (n): 0: Type 1
• Alarm output selection (T): 2: Logical OR of heater break alarm 1 and Heater break alarm 2
* Always set the maximum heater current value.
For details of Heater break alarm, refer to the separate Setting Method of Heater Break Alarm (IMR01M05-E).
Heater break alarm 1 set value
= (Maximum load current set value) × (Heater break alarm 1 set value)
= 20 A × 20 % = 4 A Heater break alarm 1 set value 4 A
Heater break alarm 2 set value
= (Maximum load current set value) × (Heater break alarm 2 set value)
= 20 A × 15 % = 3 A Heater break alarm 2 set value 3 A
The 4 and 3 amperes are set (deviation setting) to the high and low sides of the computed heater current value.
14.9 %
Current (A)
Maximum load current (20 A)
Alarm range
of heater
break alarm
Alarm range
of heater
break alarm
Heater break alarm 1 set value (upper):
20 % (4 A)
Phase angle (%)
100 % 0
No heater break alarm occurs if within this range.
However, the alarm occurs in the case of thyristor break-down.
Operation point of Heater break alarm 1 (upper)
A
larm range of Heater deterioration alarm
Operation point of Heater break alarm 2 (upper)
Computed heater current value
Operation point of Heater break alarm 2 (lower)
A
larm range of Heater deterioration alarm
Operation point of Heater break alarm 1 (lower)
Heater break alarm 2 set value (lower): 15 % (3 A)
Heater break alarm 1 set value (lower): 20 % (4 A)
Heater break alarm 2 set value (upper):
15 % (3 A)
Thyristor break-
down side
Heater break side
Delays by the same number of cycles as that when
the Number of alarm delay times is set at 1 even
with the Number of alarm delay times set at 0.