The Continuous air monitor (Alpha) is designed for monitoring airborne releases of alpha-emitting radio nuclides. The instrument comprises of an air sampler cum detector assembly and an electronic unit. The detector will be of ZnS (Ag) type. The electronic unit comprises of low voltage supplies, High voltage supply, Pre-amplifier & Amplifier, Count rate meter and Alarm generation module.
AIR-SAMPLER CUM DETECTOR ASSEMBLY :
The air sampler cum detector assembly consists of a filter holder 60mm dia., a suction chamber with two nozzles (air inlet and outlet) of size ¾ serrated and detector housing.
Air sampler is fabricated with stainless steel SS 304L. Minimum 4 numbers of threads will be provided for free and smooth fixing and removal of each part of the sampler assembly. Air sampler is designed and fabricated to achieve the particle collection efficiency more than 99% for air particles down to 0.3 micron size on glass filter paper.
Specifications for the Detector assembly for Alpha monitoring are listed below:-
Detector and size : ZnS(Ag) phosphor, 50mm dia coupled to a matched photo-multiplier with pre-amplifier.
Window Thickness : 1.5 mg/cm^2 light-sensitive pin-hole free aluminized mylar with protection against puncture.
Detector Efficiency : Not less than 25% for plutonium alpha particles over the entire window area.
SUCTION / VACUUM SYSTEM :
This Suction / Vacuum system will provide the required suction for drawing air through the filter paper in the air sampler assembly. The system comprises of a Dry type, noise-free, continuous duty, pump-motor set.
Vacuum pump-motor set:
Free air displacement :150 liters/min
Ultimate vacuum:200 mm Abs(22” Hg)
Pressure : 1.4 Kgs/cm^2 (20 lbs).
Duty : Continuous.
Electric Motor : ¾ HP, 1440 RPM with gear box, 230V AC, capacitor start, single phase TEFC B-56 frame, Class B“ insulation, continuous rating Crompton or equivalent.
Vanes : Made of self lubricant special H17 grade graphite.
Bearings : Sealed ball bearings.
Mountings : Pump and motor mounting shall be on a common base plate.
Drive : “V” belt and pulley driven (belt covered by belt guard)
Air inlet/outlet : ¼ serrated nozzles.
Vibration : Suitable anti-vibration pad.
Cooling : Air cooled.
Silencer : The pump is provided with a silencer to give noise free operation.
Pump failure alarm : Pump failure alarm indication is provided on the instrument and the same is also wired onto the remote console.
Make : M/s Tawde Engineering Works
Flow measurement and regulation:
a. The instrument is provided with a Air rotameter 50-200 lpm. with ¼ serrated SS nozzles for connection to 12 mm ID PVC tubing.
b. Rotameter is mounted in a tamper-proof manner in the air sampling line.
c. An additional rotameter is provided with necessary tubing so that the pump can be operated at the rated flow rates without overheating or excessive throttling.
d. Provision is given to discharge the hot air from the vacuum pump.
The electronic Unit comprises of a Low voltage power supply, EHT supply unit, countrate meter based on Microprocessor/microcontroller, and an audio visual alarm system.
Low voltage power supply:
The low voltage power supply unit generates the DC power supplies required for the operation of the electronic module. It has adequate line voltage and load regulation. It is also fitted with Mains line filters to avoid line interferences.
It will provide high voltage necessary for the working of the Photomultiplier tube. Its output is continuously variable from +100V to +1500V. Output is adjustable by screwdriver and EHT can be shown on the display using the detachable keypad.
Pre-amplifier and amplifier:
The Pre-amplifier & amplifier module is compatible with the ZnS Scintillation detector. It provides the amplification and shaping for the pulse signals from the detectors. The output of the amplifier is given to the Count rate meter for further data processing and display.
Unit :CPM / CPS / Bq
Ranges : 0-50000 CPM OR 0-2000 CPS OR
0-50000 Bq, with provision for unit selection and range adjustment.
Time Constant : Between 60 to 1 sec automatically varying inversely with count-rate through out the range.
Display : Auto Ranging direct reading, 6 digit 7 segment LED display & 16x2 LCD display. 6x7 LED display is interfaced using multiplexed display driver and is used for display of count-rate and hardware status indication & 16x2 LCD for visualization of preset alarm and other parameters.
Display updating : First reading on Power ON within 12 secs.
Normal (Slow): 60 sec to 12 sec automatically varying inversely with the radiation level.
Abrupt detection : Update the current reading within 1 sec and return to normal mode.
Overload : Senses overload above 200% of full scale indicates on display “OL”
Over-range : Senses if the radiation field being measured has exceeded the measurement range of the instrument and up to 200% of the instrument and displays “OFl”
Recorder output : 4 to 20 mA, with 600 ohm load.
Recorder output stability
a) Non-linearity : Max = 0.025% of Span
b) Offset current (Io=4mA) : Max = 0.0005% of Span / C
c) Span Error (Io=20mA) :Max = 0.005% of Span / C
Accuracy :+/ - 5% Full scale.
Calibration Accuracy : +/- 5% through out the range.
Testing Facilities :Provision to inject a suitable pulse generator signal for routine testing of Count rate meter shall be provided on the rear panel.
Additionally a test pulse mode through software for checking count-rate meter shall be provided
Instrument “ON” Indication : Large Area Green LED Lamp. This will indicate the Normal condition also.
Audio visual alarm system:
Alarm range :1 to full scale reading
Alarm setting : The alarm level setting shall be carried out through
RS-485 serial port with handheld configurator / PC with password protection.
Alarm Indication :
a) Red (LED) flashing large area window display
b) Loud audio tone (dual frequency tones)
Alarm annunciation scheme: As tabulated below;
Instrument Controls :
a) Acknowledgement switch for muting audio
b Reset switch for resetting the Alarm indication and alarm relay.
c) Power ON/OFF switch with Power ON indication
d) EHT ON/OFF switch is provided on front panel
Instrument Fault indication:
a) EHT failure: Visual alarm with flashing red LED indication & “EHT” message on display
b) Detector failure: Visual alarm with flashing red LED & “d-FL” message on display.
c) Microprocessor / microcontroller failure: Visual alarm with flashing green lamp.
d) Fault indications shall be cleared automatically if normal status is resumed.
Housing: The Electronic Unit is modular in structure and will be housed in rack mounted type cabinet. The module is plug in type and all the controls and display have been brought onto the front panel. The enclosure will comply with IP-21 requirements.
Remote /External Console:
a) 4 - 20 mA output linearly proportional in the entire operating range up to full scale display output. Current output will be able to drive load of 600 ohms. Output circuitry will be able to drive 200 mtrs.of twisted pair of wires.
b) Two sets of potential free contacts of Alarm relay (Change over). Contact rating 3 Amp at 250 VAC. The relay will be energized on normal condition and de-energized under alarm condition.
c) Remote alarm acknowledgement and reset signals for the field instruments.
d) Indication of instrument fault condition (detector, EHT and LV supplies failure), over range & overload conditions by up-scale 4-20 mA. (22.5 mA)
e) Pump failure alarm contact.
f) All these signals will be terminated on a 17 pin socket (Allied Connectors). The corresponding mating plug with 5 mtr cable will be supplied with the monitor.
g) RJ 45 connector for Ethernet port
h) RS-485 serial port (optional). This shall be in parallel with D-type connectors.
The monitor shall have a Ethernet 10/100 Mbps port for interfacing with a remote IBM PC-compatible computer. The features supported by Ethernet port are given below.
• The PC and the monitor shall operate in a host-slave configuration and the software protocol will be MODBUS/TCP.
• The PC as the host shall give commands and send queries. The monitor will carry out various functions in response to the queries.
• The firmware of the monitor shall be able to send the instrument data like instrument ID, instrument type, input range, display range, alarm settings, alarm status, current reading, diagnostic status of EHT/GM tube etc. to the Host PC on demand.
• The firmware shall be able to receive commands from Host PC and carry out the setting of different parameters like instrument ID, instrument type, input range, display range, alarm settings, Ack, Reset, instrument address etc.
RS485 (Optional) :
The monitor has a RS-485 Serial Communication port for interfacing with a IBM PC-compatible computer. The PC and the monitor will operate in a host-slave configuration in a multi-drop network through this interface. The PC as the host will give commands and send queries. The monitor will carry out the various functions as per the required information in response to the queries.
The firmware of the monitor will be able to send the instrument data like Instrument ID, Instrument type, Input range, Display range, alarm settings, alarm status, current reading, diagnostic status of EHT/ vacuum pump-etc. to the Host PC on demand. The firmware will be able to receive commands from Host PC and carry out the setting of different parameters like Instrument ID, Instrument type, Input range, Display range, alarm settings, Ack, Reset, EHT setting, instrument address etc. The configuration settings will be password protected and the password will be user defined.
Hand held Configurator:
a) The monitor will be supplied with a hand held configurator with RS-485 serial port interface.
b) The configurator shall be a full function LCD display terminal comprising a keyboard/navigating keys and a large alphanumeric LCD display.
c) The configurator will be capable of fully configuring and monitoring of all functions of the Continuous air monitor.
d) The configurator is not instrument specific and will be able to work in conjunction with all Continuous air monitors meeting the above specifications.
e) Dimension is such that it can be easily held in single hand. It is provided with a carrying case and shoulder belt.
f) It is operated on a rechargeable battery of long life and the battery charger is part of the supply.
g) The configuration settings are password protected and the password is user defined.
Self Diagnostics : The monitor has built-in self diagnostics. On being powered it will perform tests to ensure that all components and sub systems are functioning properly. It will check for the Power supply, High Voltage Supply, Detector, Counting and measuring circuits, Alarm Systems and Display Systems. All the alarms generated during diagnostics will be Auto Reset type.
The firmware will not halt monitoring / data acquisition function any time. The firmware is designed for high reliability and availability.
Test points shall be provided for checking the EHT voltage and for connecting external input pulse signals.
Input Power : 230VAC +/-10%, 50Hz, single phase supply. Unit is provided with protection circuitry like spike suppressor and line filter. Power ON/OFF indication is provided with an indicator LED.
Environment: The instrument is designed to be able to withstand temperature up to 50 deg C and relative humidity upto 90% in radiation areas.
Environmental compliance : As per IS 9000 / ANSI N 42.17
The instrument enclosure and detector assembly will comply with IP-21. Electronic units will withstand cumulative radiation dose of 10000 Rad. (30 years of operation).
EMI / EMC compliance: As per IEC 61000 / ANSI N42.17
Mechanical Dimensions (overall) : Size : * Height : 1500mm * Width : 650mm *Depth : 480mm
a) All the hardware like Vacuum pump, Air sampler - detector assembly, lead shielding, rotameters, Electronic unit etc are fitted in an Instrument trolley made of M.S.
b) The trolley is provided with castor wheels with locks.
c) The trolley is powder coated with DA Grey colour.
d) It will be fabricated to provide protection as per IP-20.
e) Front and Rear sides have doors with magnetic lock.
f) The vacuum pump is fitted at the bottom with guards & shock absorbers.
g) Hot air from Pump is discharged out of cabinet.
h) Two Mains supply boards with required sockets, indicators and switches / MCBs are provided inside the trolley.
i) One power board is used for Vacuum pump and the other will be used for electronic unit.
j) Internal PVC tubing shall be done between Suction head, rotameter, pump etc.