Teledyne gfc 7000ta operation manual Mother Board, 5.6. I2C Watch Dog Circuitry, To D Conversion

Theory of Operation Model GFC7000TA Carbon Dioxide Analyzer

STATUS LED’s	DC VOLTAGE TEST
	POINTS

RELAY PCA

Figure 9-15: Location of relay board Status LED’s

9.3.5.6. I2C Watch Dog Circuitry

Special circuitry on the relay board monitors the activity on the I2C bus and drives LED D1. Should this LED ever stay ON or OFF for 30 seconds, the watchdog circuit will automatically shut of all valves as well as turn off the IR Source and all heaters. The GFC wheel motor will still be running as will the Sample Pump, which is not controlled by the relay board.

9.3.6. Mother Board

This printed circuit assembly provides a multitude of functions including, A/D conversion, digital input/output, PC-104 to I2C translation, temperature sensor signal processing and is a pass through for the RS-232 and RS-485 signals.

9.3.6.1. A to D Conversion

Analog signals, such as the voltages received from the analyzer’s various sensors, are converted into digital signals that the CPU can understand and manipulate by the analog to digital converter (A/D). Under the control of the CPU, this functional block selects a particular signal input (e.g. BOX TEMP, CO2 MEAS, CO2 REF, etc.) and then coverts the selected voltage into a digital word.

The A/D consists of a voltage-to-frequency (V-F) converter, a programmable logic device (PLD), three multiplexers, several amplifiers and some other associated devices. The V-F converter produces a frequency proportional to its input voltage. The PLD counts the output of the V-F during a specified time period, and sends the result of that count, in the form of a binary number, to the CPU.

Teledyne Analytical Instruments 207