Operational Theory 2
IR7000
12
Teledyne Analytical Instruments., - Rev. 3
2.3.3 Main
Board
In effect, the main board imports an analog signal from the
preamplifier and outputs a digital signal. A lot of signal conditioning and
processing is performed along the way. Major functions of this board
include:
• Amplification
The signal from the detector is amplified
• Filter
The analog signal is filtered and conditioned
• A to D Converter
The analog signal is digitized using a voltage to frequency
converter
• Microprocessor
Encodes both the amplitude and phase of the digital signal
Counts,
integrates,
and stores the signal
Handles input and output to and from the main board
• Linearizer
Scales and linearizes the signal using data and algorithms
permanently stored in the microprocessor
• Filter
De-spikes, pre-filters and filters the signal again with a
filter rate chosen by the operator
The main board receives the raw signal from the detector and
amplifies it. In the analog circuit portion of the main board, the signal is
filtered to remove any electrical interference before passing it along to the
digital section as a relatively clean sine wave of several volts.
The sine wave is digitized using an onboard voltage to frequency
converter. In this process, both the amplitude and phase of the digital
signal are encoded and integrated. The microprocessor counts the digital
pulses and linearizes it using a 7th order polynomial whose coefficients
were determined at the factory based on the particular detector.