Figure 13-16: Heater Control Loop Block Diagram - Teledyne T200 Operation Manual

Principles of Operation
13.3.4.4. HEATER CONTROL
314
Teledyne API – T200 NO/NO2/NOx Analyzer Operation Manual
For a variety of reasons such as, efficiency of certain chemical reactions, stabilization of
sample gas temperature and pressure, etc., various subcomponents of the T200 are
heated/cooled.
Two types of sensors are used to gather temperature data for the CPU:

THERMISTORS: These are used in areas where the temperature control point is at
or near ambient temperature (e.g. the reaction cell temperature, internal chassis
temperate).

Thermistors change resistance as they heat up and cool down. A DC signal is
sent from the Mother board of a sent voltage and current. As the thermistor
changes resistance, the returning voltage rises and falls in direct relationship to
the change in temperature.

The output signal from the thermistors is received by the motherboard,
converted into digital data which is forwarded to the CPU.

THERMOCOUPLES: These are used where the target temperature is high such as
the NO  NO converter.
2

Thermocouples generate DC voltage that rises and falls as the thermocouple
heats up and cools down.

This DC signal interpreted, conditioned and amplified by the Relay PCA then
transmitted to the motherboard where it is also converted into digital data and
forwarded to the CPU.
All of the heaters used in the T200 are AC powered which are turned ON/OFF by AC
Relays located on the relay PCA in response to commands issued by the CPU.
Thermistor(s) –
Reaction Cell, Optional Internal
Span Gas Generator, Optional O
Sensor)
J-type
Thermocouple
( NO  NO converter)
2
Not used
on the T200
Reaction Cell

Figure 13-16: Heater Control Loop Block Diagram.

2
RELAY PCA
THERMOCOUPLE
CONFIGURATION
JUMPER
(JP5)
Solid State
AC Relays
DC Control Logic
(for DC heaters)
 NO
NO
2
Converter
Heater
Heater
MOTHER BOARD
Thermistor
interface
Preamplifiers
and Signal Converter
Conditioning
Cold Junction
CPU
Compensation
Other Optional
AC HEATERs
(Internal Span Gas
Generator;O2 Sensor)
06858E DCN7057
A/D
(V/F)