Teledyne 7300A manual 3.5Digital Signal Processing & Electronics, Start-upand Theory of Operation

3 Start-up and Theory of Operation Model 7300A

3.5Digital Signal Processing & Electronics

The Model 7300A uses an 8031 microcontroller (Central Processing Unit—CPU) with 32 kB of RAM and 128 kB of ROM to control all signal processing, input/output, and display functions for the analyzer. System power is supplied from a universal power supply module designed (C65507) to be compatible with any international power source. (See Major Internal Components in chapter Maintenance for the location of the power supply and the main electronic PC boards.)

The Temperature Control board (C69535A) is set to a single voltage

(110 or 220 VAC) and set the temperature of the sampling system at 45oC. The signal processing electronics including the microprocessor, analog to digital, and digital to analog converters are located on the Motherboard (C67435B) on side of the case.

The detector output level depends on the intensity of the IR source, the length of the cell and the type of fluid in the cell. Usually the output is between 0.2 and 0.9 mVDC. The Teledyne detector consists of four detec- tors: A, B, C and D. They are strapped to the inputs of the positive, very high-gain amplifiers U1, U2, U3, and U4. Amplifiers U1 through U4 are high quality, very low offset amplifiers.

Preamplified signals (usually between .2 to 1.0 volt) are delivered via the ribbon cable to the measuring board through an 8-point dip switch. Connectors deliver power from the measuring board to the amplifiers and 300–450 mADC current to the IR source.

The motherboard serves as a power distribution and interface board.

The Auto-Zero amplifier PCB board is mounted on top of the Motherboard. These boards are accessible by sliding the system out of the case after removing the screws on the back plate.

The Temperature Control Board keeps the temperature of the measur- ing cell regulated to within 0.1 degree C. A thermistor is used to measure the temperature, and a zero-crossing switch regulates the power of the heaters inside the sample chamber. The result is a sensor output signal that is tem- perature independent.

The output of the preamp is fed to variable gain amplifier, which provides automatic range switching under control of the CPU. The output from the variable gain amplifier is sent to an 18 bit analog to digital con- verter.

The digital concentration signal along with input from the control panel is processed by the CPU and passed on to the 12-bit DAC, which outputs 0-

1V dc Concentration and Range ID signals. An voltage-to-current converter provides 4-20 mA dc concentration signal and range ID outputs.

3-6 Teledyne Analytical Instruments