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Field Programmable Analog Arrays based Leak Detector Remote Terminal Unit

for Fast Breeder Reactors

Conference Paper · February 2014

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Field Programmable Analog Arrays based Leak Detector Remote Terminal Unit for Fast Breeder

Reactors

Sanga Ramesh*, P.Sahoo, N.Murali and S.A.V Satya Murty Real Time Systems Division, Electronics, Instrumentation and Radiological Safety Group,

Indira Gandhi Centre for Atomic Research, Kalpakkam-603102, India *Email: stram@igcar.gov.in

Abstract— Leak Detector Remote Terminal Unit (LDRTU) is a single board, embedded system that is used to acquire analog signals from leak detectors of secondary sodium loop in Fast Breeder Reactor (FBR). This unit sends digitized data packets to the nearest Local Control Centre (LCC) and generates control outputs in the form of potential free contacts during all states of reactor operation. The design of analog circuitry in the above LDRTU was realized with multiple numbers of discrete components like multiplexers, amplifier, filter and analog to digital converter. This paper presents the design implementation of Field Programmable Analog Array (FPAA) based LDRTU in which the complete analog circuitry with discrete components are replaced by FPAA. The functionality of the above circuitry is realized with this miniaturized FPAA chip. This design technique overcomes the problems like obsolescence of components along with the added advantage of improved reliability, reduced board space and power consumption. This paper also demonstrates the performance of developed LDRTU with simulated sodium leak detector inputs. Index Terms— Embedded Systems, Field Programmable Analog Array, Leak Detector Remote Terminal Unit, Fast Breeder Reactor

I. INTRODUCTION

The 500 MWe capacity sodium cooled Proto type Fast Breeder Reactor (PFBR) has been designed which is under advanced stage of construction at Kalpakkam, Tamilnadu, India. The reactor will be in operation in near future. Besides this, three more FBRs are planned to be constructed. In FBR sodium is used as coolant, because of its good heat transfer and nuclear properties like high thermal conductivity, reasonable specific heat, low neutron moderation and absorption, and high boiling point at near atmospheric pressure [1]. The primary and secondary loops of FBR uses large inventory of sodium as coolant. Leaks in sodium systems have the possibility of being extremely hazardous due to the vigorous reaction of liquid sodium with oxygen and water vapour in the air. Trace of liquid sodium leaked from the pipeline catches fire immediately. It is necessary to detect the leaks at an early stage. Different types of leak detectors are used in PFBR for detecting sodium leak [2]. The LDRTUs are used to get analog signal from leak detectors and sends the leak detection status to the operator for necessary action in order to prevent the damage of different equipments in the PFBR. Hence the design of LDRTU plays a key role in fast reactor safety. LDRTU is a single board, microcontroller based real time remote data acquisition & control system. It is used in Sodium Cooled Fast Breeder Reactors to acquire analog signals from the sodium leak detector processes and sends digitized data packets to the nearest Local Control Centre (LCC) and to generate control DOI: 02.LSCS.2014.8.37 © Association of Computer Electronics and Electrical Engineers, 2013

Proc. of Int. Conf. on Advances in Communication, Network, and Computing, CNC

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outputs in the form of potential free contacts during all states of the reactor operation [3]. The analog signal conditioning circuit required to the above data acquisition system is realized with multiple numbers discrete ICs such as multiplexer, amplifier, filter and analog to digital converter. This design includes operational amplifiers, voltage references and passive components which require more power, space, prone to parameter changes like gain, cut-off frequency with respect to temperature, aging effect, prone to parasitic capacitance effect, less reliable due to more number of components and interconnections on the board. Hence a possible approach to solve the problems of discrete component based analog signal conditioning circuit is by introducing FPAA based instrumentation. The FPAA is a general-purpose, digitally reconfigurable analog signal processing chip [4]. Its current commercial applications centre on signal conditioning and rapid prototyping [5]. With its dynamic reconfigurability, fast analog signal processing speed, FPAA can be used in real time embedded systems [6]. Moreover, the convenient software design environment provided with FPAA evaluation kits and its dynamic reconfigurability make it attractive for developing embedded systems [5]. These advanced devices offer an attractive way of reducing cost, size and complexity of the analog signal conditioning circuits. The analog circuits based on FPAA can perform multiple functions; adjust to different environmental conditions [7]. The resulting designs require minimum hardware, time, convenient to prototype and are highly reliable. This paper presents the design implementation of the LDRTU analog signal conditioning with single FPAA chip. This design and development activity include the design and simulation of analog circuits of LDRTU using FPAA CAD tool, testing of the designed analog circuit using FPAA development board, design configuration interface to explore the feature of FPAA such as dynamic reconfiguration [8]. Finally the performance of FPAA based embedded system was tested in simulation facility by giving leak detector inputs and the result is shown in PC hyper terminal.

II. BRIEF DESCRIPTION OF LDRTU

The LDRTU accesses the voltage signal from the output of the leak detector, processes and sends the status such as leak, no leak, cable open and cable short to the local control centre to take necessary action by operator. The block diagram of LDRTU is divided into (i) Input (I/P) section and (ii) microcontroller section. The I/P section consists of analogue signal conditioning such as Multiplexer, Amplifier, Low pass Filter and Analog to Digital Converter where as the Microcontroller section consists of Microcontroller, Memory, Reset, Buffer, Ethernet, and RS232 as shown in Fig.1.

Figure.1. Block diagram of LDRTU

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Figure.2. Illustration for implementation of LDRTU I/P Section inside FPAA

The entire analog signal conditioning circuit of the LDRTU includes the resistive network from sodium leak detector excited with 5V power supply [2], multiplexers to select the input, amplifier to strengthen the leak detector signal, butter worth low pass filter to remove the high frequency noise and ADC. Fig.2 shows the overall analog signal conditioning circuit of LDRTU.

III. IMPLEMENTATION OF I/P SECTION WITH FPAA

FPAAs are VLSI devices built by using operational amplifiers, capacitors, switches and static RAMs in a single silicon ship [9]. Once the analog signal conditioning circuit to be designed is fixed, the design can be implemented by changing the capacitance values in the RAM array. Thus, taking the advantage of the switched capacitor technology [10], a wide variety of analog blocks like amplifiers with varying specifications can be realized by only changing the capacitance values. The FPAA configuration is performed by means of FPAA CAD tool, in which user can draw the desired analog circuit and send the related data block to FPAA device through RS232/USB communication [8]. The received data can be stored in the FPAA of RAM, in order to set the internal capacitance according to the designed analog circuit.

Figure. 3. The designed analog circuit using FPAA CAD tool

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Figure.4. Simulated results using FPAA CAD tool

In the proposed design, an FPAA has been used to realize analog signal conditioning of LDRTU, whose main building blocks are: 1) an amplifier to strengthen the leak detector signal, 2) a low pass filter with 500 Hz cut off frequency to remove the high frequency noise, 3) an analog to digital converter, and 4) multiplexing. The designed circuit using CAD tool is shown in Fig.3. Dynamic reconfiguration feature of FPAA is used to implement the multiplexing of inputs from the leak detectors. Before designing actual FPAA based LDRTU the analog signal conditioning circuit is tested by using CAD tool and the FPAA development board. In this process the circuit topology along with default set parameters of each configurable module known as the primary configuration is sent to the FPAA through serial communication port to the development board. Then it starts working as soon as power -on reset. The satisfied performance of the configured design is shown in Fig.4. The FPAA is usually configured by means of CAD tool, whose graphical interface allows constructing analog circuit quickly and easily by selecting, placing, and wiring the selected configuration analog modules. The primary configuration data is used to configure the FPAA. The main limitation of FPAA is that it can be used with only one input at a time. To implement multiplexing, the dynamic reconfiguration (on the fly configuration) is required but it is not possible with FPAA CAD tool. In order to do so micro controller has to be used. Any way the CAD tool provides C code that enables the reconfiguration of FPAA through the host microprocessor. For this purpose configuration interface is to be provided between microcontroller and FPAA.

Figure.5. Configuration interface between microcontroller and FPAA

Microcontroller configures FPAA, implementing a synchronous serial protocol, through its I/O lines such as CS2b, DIN, ERRb, Activate, Execute and DCLK as shown in Fig.5. Dynamic reconfiguration, as mentioned above, allows changing the parameters of implemented analog blocks without modifying the circuit topology. Compared with primary configuration, the “on the fly configuration” to be transmitted is faster, since the lower amount of data is required.

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IV. SOFTWARE IMPLEMENTATION

The software of the LDRTU to perform the required functioning is developed using embedded C program. It is divided into three steps 1) To configure the FPAA with primary configuration, 2) To read the serial ADC data, 3) To process the data and send the leak, no leak, cable open, and cable short, and 4) To configure the FPAA with reconfiguration data to implement multiplexing. As illustrated in Fig.6, the measurement procedure, implemented by the proposed software architecture, consists of different stages, details of which are given below.

A. Initialization The first stage of the software is initialization of the microcontroller and the primary configuration of the FPAA. In this section the timers of microcontroller and the configuration interface are performed. FPAA is reset by setting the microcontroller pin associated to FPAA pin. Then microcontroller transmits the primary configuration data to the FPAA, through configuration interface. The input channel of the LDRTU is selected as channel one by default.

Figure.6. Flow diagram of measurement process of LDRTU

B. Measuring of the signal and digitization The five different types of signals to validate the status like sodium leak ,sodium no leak, cable open, cable short and cable healthy from the leak detector is processed by FPAA analog blocks such as amplifier, low pass filter and ADC. The serial ADC signal from the FPAA is captured by the microcontroller with serial interface between microcontroller and FPAA.

C. Sending the leak status to LCC The captured digital signal from the FPAA is processed by the microcontroller to know the status of the signal. The status like leak, no leak, cable short, and cable open is calculated by the microcontroller and sent to the nearest local control centre (LCC).

D. FPAA reconfiguration. The kiel software is written for sending the leak detector status to the LCC, the input channel of the LDRTU is incremented to channel 2, the FPAA is reconfigured with reconfiguration data stored in the microcontroller memory, and the process continues up to channel seven and then come backs to the channel one.

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V. EXPERIMENTAL SETUP & TEST PERFORMANCE OF LDRTU

The designed LDRTU performance is tested with different leak detector input signals like leak, no leak, cable open, cable short. Towards this the different simulated inputs of leak detector are given through resistive network to the LDRTU. The Experimental setup of LDRTU using FPAA and Microcontroller is shown in Fig 7.This is the total functional block diagram of the developed FPAA based LDRTU. The required analog signal conditioning blocks like multiplexer, amplifier, filter and ADC of LDRTU are synthesized using single FPAA In this setup all the devices require 5V power supply only whereas in earlier design [3] two independent power supply units of 12V, 5V were used for analog section and digital section respectively.

Figure.7. Block diagram of the present LDRTU experimental setup using FPAA

TABLE I. THE PERFORMANCE TEST OF THE LDRTU

S.NO CHANNEL NO STATUS 1 LEAK DETECTOR 1 LEAK 2 LEAK DETECTOR 2 NO LEAK 3 LEAK DETECTOR 3 CABLE SHORT 4 LEAK DETECTOR 4 CABLE OPEN 5 LEAK DETECTOR 5 CABLE HEALTHY 6 LEAK DETECTOR 6 NO LEAK 7 LEAK DETECTOR 7 CABLE HEALTHY

The test performance is done in the following steps 1) The leak detector signal is given to FPAA input through resistive network, 2) The FPAA is configured for channel one of LDRTU, 3) The analog signal is processed with the FPAA, 4) The microcontroller reads the FPAA serial ADC and finds the five different statuses of the leak detector signal, and 5) The results of the LDRTU are observed in hyper terminal of the PC. The performance of FPAA based LDRTU is shown in table I.

VI. CONCLUSION

The FPAA based RTU design was introduced for leak detection of liquid sodium, where an FPAA was chosen in place of conventional discrete analog components. Several experiments were conducted with hardware development platform and based on the knowledge gained; a real prototype board was developed and tested successfully. In future it is planned to deploy this concept for various application specific embedded systems. For digital portions like microcontrollers, decoders, buffers, and other required hardware, the concept of FPGA (Field Programmable Gate Arrays) is being deployed which will reduce the digital ICs in the design. The present design miniaturizes the instrumentation by reducing the power supply units, power consumption, PCB size which in turn improves the functionality and reliability of the instrument. The FPAA

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approach has been deployed towards development of instrumentation for leak detection which will be used in Fast Breeder Reactor to get information regarding sodium leak. The implementation of such device will reduce the hardware components by making the instrument more compact. In addition we have initiated this development program to make FPAA based pH meter and compact as well as reliable instrumentation for temperature monitoring using thermocouple which will be extremely useful for any industrial set up.

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