MKS Baratron 631D, Инструкция по эксплуатации, Страница: 48 / 64

Chapter Four: Operation
40
Heater Status LEDs and Heater Alarm Relay
The 631D transducer is designed to function at its specified operating temperature by maintaining
the sensor temperature within a tight range of the operating temperature. There are two status
LEDs, “Htr Fail Status” and “At Temp Status,” that provide a visual indication of the heater
condition. Since the operating temperature of the sensor is critical, the 631D unit contains a
heater alarm relay that monitors the performance of the sensor heater. In addition, the Interface
(J1) connector contains the heater alarm relay contact pins. (Refer Table 6: Pinout of the
Interface Connector (J1), page 34, for the pinout of the Interface (J1) connector and refer to Table
9, page 41, for a summary of the conditions determining the heater status LEDs and heater alarm
relay output.)
When power is applied to the unit, the heater receives full power and the temperature of the
sensor rises toward the nominal operating temperature. The heater alarm relay will be energized
to indicate that the heater is working. During the warm-up period, the “Htr Fail Status” LED will
be off and the “At Temp Status” LED will glow yellow.
When the actual temperature of the sensor is within the LED temperature window, 631D heater is
in control and the “At Temp Status” LED will glow green. The heater alarm relay will continue
to be energized and the “Htr Fail Status” LED will continue to be off. Note that the LED
temperature window is approximately within 8% of the operating temperature, 150

C or 200

C,
and is used for a gross indication the sensor is within acceptable limits. The actual operating
temperature of the sensor is maintained within a significantly tighter range.
If the heater control circuitry fails in a no-current failure mode, the sensor will begin to cool. At
this time, the “Htr Fail Status” LED will glow red and the heater alarm relay will be de-energized.
When the sensor temperature falls below the lower limit of the operating temperature LED
window, the “At Temp Status” LED will glow yellow.
If the heater control circuit fails in a always-‘On’ mode, the sensor will overheat. The “At Temp
Status” LED will glow yellow when the sensor temperature reaches the upper limit of the LED
temperature window, the “Htr Fail Status” LED will continue to be off and the heater alarm relay
will continue to be energized.
Over-Temperature Protection
The heater implements two temperature sensors, one dedicated to the heater control circuit and
one dedicated to the over-temperature protection. The over-temperature protection limit is used
as one layer of protection by the heater alarm circuit, refer to Table 8: Over-Temperature Cutoff
Value for the over-temperature value for each of the operating temperatures. If the transducer
temperature reaches the over temperature cutoff, the “Htr Fail Status” LED will glow red, the
heater alarm relay becomes de-energized and the “At Temp Status” LED will glow yellow. Note
that once the temperature drops below the overtemperature cutoff, the heater power will be
activated, the heater alarm relay energized, the “At Temp Status” LED will continue to glow
yellow and the “Htr Fail Status” LED will turn off.
Operating Temperature
(

C)
Over-Temperature
Value (

C)