Motherboard; A To D Conversion; Sensor Inputs - Teledyne T200 User Manual

M
OTHERBOARD
This PCA provides a multitude of functions including, A/D conversion, digital
input/output, PC-104 to I
through for the RS-232 and RS-485 signals.

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 (A/D) converter. 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 converter consists of a Voltage-to-Frequency (V-F) converter, a Programmable
Logic Device (PLD), three multiplexers, several amplifiers and 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, 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 this
analyzer it is used in unipolar 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.

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: The PMT detector output from the PMT preamplifier is
used in the computation of the NO, NO
Dashboard and reported through the instrument's analog outputs and COM ports.
HIGH VOLTAGE POWER SUPPLY (HVPS) LEVEL: The PMT high voltage is based
on the drive voltage from the preamplifier board. It is digitized and sent to the CPU which
then calculates the voltage setting of the HVPS.
PMT TEMPERATURE: The PMT temperature is measured with a thermistor inside the
PMT cold block. Its signal is amplified by the PMT temperature feedback circuit on the
preamplifier board and is digitized and sent to the CPU which calculates the current
temperature of the PMT.
SAMPLE GAS PRESSURE SENSOR: Located on the flow/pressure sensor PCA, this
sensor measures the sample chamber's gas pressure.
198 Teledyne API T200 NO/NO
2 C translation, temperature sensor signal processing and is a pass
and NO
X
/NO Analyzer with NumaView™ Software
2 x
concentrations displayed in the
2
083730200A DCN7962