Yokogawa EJX930A - Manual (Page 166)

A8-22
IM 01C25T02-01E
A8.3 Heat Trace Monitoring
The EJX with Heat trace monitoring function
calculates the flange temperature by using the two
temperature sensors built in the EJX. An analog
alert is generated if the temperature reached to the
preset level.
The flange temperature is based on the following
parameters and calculation formula.
[Parameters]
Parameter name Explanation
CAP_TEMP_VAL (CT) Measured capsule
temperature value
AMP_TEMP_VAL (AT) Measured amplifier
temperature value
FLG_TEMP_VAL (FT) Flange temperature value
(Calculated value)
FLG_TEMP_COEF (Cf) Coefficient to calculate flange
temperature
FLG_TEMP_H_LIM Threshold to generate Flg
Temp High Alarm
FLG_TEMP_L_LIM Threshold to generate Flg
Temp Low Alarm
Amplifier
Temperature
Capsule
Temperature
SENSOR Transducer Block
PRIMARY_VALUE
AMP_TEMP_VAL
CAP_TEMP_VAL
Calculation of
FLANG_TEMP_VAL
FLG_TEMP_COEFF
CT + (CT - AT) x Cf
Heat Trace Monitoring
FLG_TEMP_H_LIM
FLG_TEMP_L_LIM
FLG_TEMP_VAL
DIAG_ERR
DIAG_OPTION
ALM_SUM.disadle
DIAG_PRI
FLG_TEMP_ALM
Alarm and Alert
AI function
Block
CHANNEL=1
CHANNEL=5
CHANNEL=4
HI_LIM
LO_LIM
Resorce
Block
DEVICE_
STATUS[7]
LCD
FA0810.ai
CHANNEL=6
Figure A8.8 Functional Block Diagram of Heat Trace Monitoring
[Calculation formula]
FLG_TEMP_VAL(FT) = CT + C
f
× (CT - AT)
The FLG_TEMP_VAL (FT) is assigned to Process
Value (PV) in the AI function block. If the flange
temperature exceeds the value preset to the
HI_LIM, LO_LIM, HI_HI_LIM, or LO_LO_LIM in the
AI function block, an analog alert is generated.
NOTE
The flange temperature is calculated by the
calculation formula assumed that the capsule
part of EJX is heated up or kept warm by an
electrical heater or steam. In the case of an
atmosphere temperature or less, the difference
of temperature of approximately 3 to 4°C
may occur because the amplifier temperature
becomes higher than the capsule temperature.