Yokogawa EJX930A - Manual (Page 71)

<4. Diagnostics>
4-21
IM 01C25R02-01E
4.2.3 Heat Trace Monitoring
The EJX multivariable transmitter with Heat
trace monitoring function calculates the flange
temperature by using the two temperature sensors
built in the EJX multivariable transmitter.
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 (CT) Measured capsule temperature
value
Amp temp (AT) Measured amplifier temperature
value
Flg temp (FT) Flange temperature value
(Calculated value)
Flg temp Coef (Cf) Coefficient to calculate flange
temperature
Flg temp Hi Alert Val Threshold to generate FT high
alarm
Flg temp Lo Alert Val Threshold to generate FT low
alarm
[Calculation formula]
Flg temp (FT) = CT + Cf X (CT-AT)
If the flange temperature exceeds the value preset
to Flg temp Hi Alert Val or Flg temp Lo Alert Val,
an alert is generated.
NOTE
The flange temperature is calculated by the
calculation formula assumed that the capsule
part of EJX multivariable transmitter 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.
4.2.3.1 Flg Temp Coef Setting
The value calculated according to the following
procedure is set to Flg temp Coef.
• To enhance the calculation accuracy of the
flange temperature, measure the actual flange
temperature by using the temperature sensor
etc.
• Calculate the ratio of the capsule temperature
to the capsule temperature minus the amplifier
temperature from the two temperature values
measured by EJX multivariable transmitter.
• Derive the Flg temp Coef from the measured
flange temperature and the ratio of the capsule
temperature to the amplifier temperature in
accordance with the following calculation
formula.
Flg temp Coef (Cf) =
(Actual measured value of Flange temperature) - CT
CT - AT
For DTM (HART 5), Flg Temp Coef parameter can
be set by using Tuning function.
By setting the measured value of flange
temperature, Flg Temp Coef is calculated by using
capsule temperature and amplifier temperature.
• Procedure to call up the Tuning display.
Diag and Service → Advanced Diag Configuration →
Heat Trace → Tuning