Teledyne 3190 manual Block Diagram of the Signal Processing Electronics

2 Operational Theory Model 3190

Figure 2-3: Block Diagram of the Signal Processing Electronics

In the presence of oxygen the cell generates a current. A current to voltage amplifier (I–E AMPL) converts this current to a voltage.

The second stage amplifier (TEMP COMP) supplies temperature compensation for the oxygen sensor output. The temperature compensation amplifier incorporates a thermistor (THERM) that is physically located in the cell block. The thermistor is a temperature dependent resistance that changes the gain of the amplifier in proportion to the temperature changes in the block. This change is inversely proportional to the change in the cell output due to the temperature changes. As a result there is negligible net change in the signal due to temperature changes once the sensor comes to equilibrium. See Specifications in the Appendix.

The output from the temperature compensation amplifier is sent to an analog to digital converter (ADC), and the resulting digital concentration signal is sent to the microcontroller.

The digital concentration signal along with input from the front panel buttons (KEYBOARD) is processed by the microcontroller, and appropri- ate output signals are directed to the display, alarm relays, and RS-232 output. The same digital information is also sent to a 12-bit digital to analog converter (DAC) that produces the 0-10 V dc analog concentration signal and the 0-10 V dc analog range ID output. A current to voltage converter (E–I CONV) produces the 4-20 mA dc concentration signal.

2-6 Teledyne Analytical Instruments