12-11-2012, 03:43 PM
A REPORT ON THERMOCOUPLE SIGNAL CONDITIONING USING FPAA
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ABSTRACT
The aim of the project is to study the FPAA technology w.r.t. the architecture, programming and application. Field Programmable Analog Array (FPAA) is a flexible integrated chip which has configurable analog blocks which can be used to build almost any analog circuit design on a single chip. FPAAs have revolutionized the field of analog electronics. FPAA available in the lab is Anadigm AN221E04.
An analog design was thus developed for thermocouple signal conditioning in Anadigm designer tool. Signal Conditioning such as amplification, linearization, offset removal etc were achieved using FPAA. The output of FPAA was given to the Voltage-to-frequency (V-to-F) converter already developed in the Innovative Instrumentation Section(IIS) for converting voltage to Frequency. The Pulses coming from V-to-F converter were counted by a pulse counter using 8051 microcontroller and 8254 Programmable Interrupt Timer.
For data acquisition from pulsating sensors, time-stamping of data was also achieved using an internal timer/counter of AT89C55WD microcontroller. The frequency and the time elapsed were sent to the PC via RS232 serial communication. A Graphical User Interface was developed in Matlab for data acquisition, features like storing data in file, plotting a graph for elapsed time vs frequency were included.
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Pulsating sensors developed in IIS
In the Innovative Instrumentation Section (IIS) of Indira Gandhi Centre for Atomic Research (IGCAR), non-conventional type high performing pulsating sensors have been developed and they are deployed in many laboratory and industrial applications.
These are constructed in such a way that the output signal generated from sensor head is a train of rectangular pulses. These pulses are directly sent to PC or any standalone system to give information on pulse frequency which is directly related to temperature. Sensors at IIS are designed to respond very sensitively to shifts in one of the four electrical properties namely, (i) ionic or electronic conductance, (ii) dielectric permeability, (iii) inductance, and (iv) electromotive force (emf) of the physical or physico-chemical systems to be probed. These four different classes of sensors, individually or in combination, offer an extensive scope for monitoring diverse parameters. Any parameter that causes change in any of the above property, directly or indirectly, becomes measurable. Measurements with the pulsating sensors involve counting the digital pulses for a desired duration for determination of frequency by an appropriate digital device.
Introduction to the project
Thermocouple signal conditioning was done with the help of FPAA chip. This is a recent technology in analog world which is described later. The Amplified, filtered and linearized output from the FPAA was then given to the V-to-F converter that converts voltage to rectangular pulses that can be easily read by the pulse counter module to calculate the corresponding frequency. In addition to frequency calculation, I also programmed the microcontroller to estimate the time elapsed using internal timer of 8051 and was able to send it
to PC along with frequency value. For data acquisition in PC, interfaces were already developed in C and Visual Basic but a need was felt to get the data in some user-friendly and flexible language. So, a graphical user interface was developed in MATLAB for data acquisition.
Architecture of FPAA
In this project, all the work has been done on discrete time FPAAs. Hence, the architecture of discrete time FPAAs shall be looked into. As mentioned earlier, the heart of discrete time FPAAs is the switched capacitor technology. On this technology are built the Configurable Analog Blocks (CABs) which make up most of the chip. Apart from these, there are Input/Output cells, Look-Up Tables (LUTs) and Successive Approximation Registers (SARs).
Since the Anadigm IC AN221E04 was used for all practical purposes, the figures used to supplement the text would be specific to this IC.
the FPAA
All dynamically programmable Analog Signal Processing (dpASP) parts need configuration information loaded when the device first powers up (static configuration). Some devices have an additional feature to allow you to change the active configuration while device is operational (dynamic re-configuration). An FPAA can load itself as a SPI master from an FPGA EPROM or from a SPI. It can also load as a slave from a processor. Multiple devices can be loaded from the same EPROM or processor.
Data is sent to shadow SRAM first. It is then loaded into the configuration SRAM after one clock cycle. As part of the power-on reset sequence, SRAM is cleared to a known (safe) state. It is the job of the configuration logic to transfer data from the outside world into the Shadow SRAM and from there, copy it into the Configuration SRAM.
Sensor Signal Conditioning using FPAA
The main challenge in the sensor signal conditioning is to develop a system that can easily modify the sensor output as required with good accuracy and linearity. Using FPAA this purpose can be achieved easily. FPAA introduces a radical software-centric approach to analogue circuit design where easy-of-use is a major feature. Because FPAA is programmable and reconfigurable, just one device can provide multiple sensor conditioning circuits under the real-time control of a digital microprocessor. Sensor signal linearization, offset compensation, calibration, and signal modulation circuits can now be implemented in minutes on a drift-free integrated silicon platform. FPAA can provide the sensor signal conditioning with an alternative
solution. Design of the system using FPAA involves: (1) Amplification, offset removal and
linearization of the signals from sensors; (2) Simulation using FPAA software before using the
circuits for real time system; (3) Interfacing the Sensor system with the FPAA; (4) Carrying out
test in order to condition the signal obtained from different sensors.