Teledyne 9110T instruction manual Teledyne Analytical Instruments 349

Model 9110T NOx Analyzer Principles of Operation

13.3.4.4. Heater Control

For a variety of reasons such as, efficiency of certain chemical reactions, stabilization of sample gas temperature and pressure, etc., various subcomponents of the 9110T 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 NO2  NO converter.

∙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 9110T are AC powered which are turned ON/OFF by AC Relays located on the relay PCA in response to commands issued by the CPU.

Figure 13-18: Heater Control Loop Block Diagram.

Teledyne Analytical Instruments 349