Motherboard; A To D Conversion; Sensor Inputs - Teledyne 100E Instruction Manual

Theory Of Operation Model 100E Instruction Manual
has stopped functioning, the Watchdog Circuit will automatically shut of all valves as well
as turn off the UV Source(s) and all heaters. The Sample Pump will still be running.

10.4.10. Motherboard

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

10.4.10.1. 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 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.
The A/D can be configured for several different input modes and ranges but in the is
used in uni-polar mode with a +5V full scale. The converter includes a 1% over and
under-range. This allows signals from -0.05V to +5.05V to be fully converted.
For calibration purposes, two reference voltages are supplied to the A/D converter:
Reference ground and +4.096 VDC. During calibration, the device measures these two
voltages, outputs their digital equivalent to the CPU. The CPU uses these values to
compute the converter's offset and slope and uses these factors for subsequent
conversions. See Section 6.7.4.6 for instructions on performing this calibration.

10.4.10.2. Sensor Inputs

The key analog sensor signals are coupled to the A/D through the master multiplexer
from two connectors on the motherboard. 100K terminating resistors on each of the
inputs prevent cross talk from appearing on the sensor signals.
PMT DETECTOR OUTPUT: This signal, output by the PMT preamp PCA, is used in the
computation of the SO , SO and SO concentrations displayed at the top right hand
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corner of the front panel display and output through the instruments analog outputs and
COMM ports.
PMT HIGH VOLTAGE POWER SUPPLY LEVEL: This input is based on the drive voltage
output by the PMT pram board to the PMT's high voltage power supply (HVPS). It is
digitized and sent to the CPU where it is used to calculate the voltage setting of the HVPS
and stored in the instruments memory as the test function HVPS. HVPS is viewable as a
test function (Section 6.2.1) through the analyzer's front panel.
186 045150102 Rev XB1