The electronic unit comprises of low voltage power supply, High voltage supply, Pre-amplifier & Amplifier, Count rate meter and Alarm generation module. The electronic unit and the detector assemblies are mounted inside a single floor mounted trolley.
(A)Air-Sampler cum Detector Assembly (Alpha and Beta):
The air sampler cum detector assembly for alpha consists of a filter holder 60mm dia., a suction chamber with two nozzles (air inlet and outlet) of size ¼ serrated and detector housing.
Air samplers are fabricated with stainless steel SS 304L. Air sampler is designed and fabricated to achieve the particle collection efficiency better than 97% for air particles down to 0.3 micron size on glass filter paper.
Dual scintillator based detector assembly measures simultaneously both alpha and beta activity present in a given sample separately. It uses ZnS(Ag) scintillator deposited on plastic scintillation material and coupled to a 2 PMT. To minimize the gamma background adequate lead collar / brace shielding has been provided.
PERFORMANCE WITH ALPHA SOURCE:
Efficiency for alpha (Guaranteed): with calibrated Am241 standard source > 25%.
Standard source used: Eckert and Ziegler make alpha wide area reference source of activity 1.020KBq.
Beta cross talk (counts in Beta channel) while counting with alpha source alone < 2.5%.
PERFORMANCE WITH BETA SOURCE: Efficiency for beta: with calibrated Sr90/Yt90 combined efficiency standard reference source > 25%.
Cross talk: Counts into alpha channel < 0.2%
Standard source used: Eckert and Ziegler make beta wide area reference source of activity 1.13KBq.
(B) Vacuum pump-motor set: Free air displacement: Better than 115 liters/min.
Ultimate vacuum: 200 mm Abs (22 Hg). Pressure: 1.4 Kgs/cm^2 (20 lbs)
Electric Motor : ¾ HP, 1440 RPM with gear box, 230V AC, capacitor start, single phase TEFC B-56 frame, Class B insulation, continuous rating.
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 a 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: Gast Inc, USA.
Count-rate meter: The count rate measurements are carried out by the Data acquisition unit from the corresponding radiation type detected by the Dual scintillator detector. Important features of the countrate meter are listed below.
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: Color TFT Display is used for display of count-rate and hardware status indication & for visualization of preset alarm and other parameters.
Display updating: First reading on Power ON within 12 secs.
Time Constant: 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 and indicates on display OL
Over-range: Senses if the radiation field being measured has exceeded the measurement range of the instrument and upto 200% of the instrument and displays OFl. inject.
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% throughout the range.
Testing Facilities: Provision to Feed a suitable pulse generator signal for routine testing of Count Rate meter will be provided on the rear panel. Additionally a test pulse mode through software for checking count- rate meter will be provided Audio Visual.
Alarm system: The instrument indicates Alarm status on the TFT display for Active and Normal conditions. Two sets alarm relays will be provided. Alarm range: 1CPS/CPM/Bq to full scale reading Alarm setting: The alarm level setting will be carried out through Ethernet port with PC with password protection.
Alarm Indication : a) Red flashing large area window display on TFT display b) Loud audio tone (single / dual frequency tones)
Alarm annunciation scheme: As tabulated below;
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 the front panel.
Instrument Fault indication:
a) EHT failure: Visual alarm with flashing red Eht message on TFT display
b) Detector failure: Visual alarm with flashing red d-Fl message on TFT display.
c) Microprocessor / microcontroller failure: Visual alarm with flashing green lamp.
d) Fault indications are cleared automatically if normal status is resumed.
Housing: All the modules of the Electronic unit will be housed in rack mounted type cabinet . The modules are plug in type and all the controls and display are available on the front panel.
Remote / External Console: The instrument is provided with two remote console connectors for the two channels.
a) 4 - 20 mA linear proportional 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-energised under alarm condition.
c) Remote alarm acknowledgement and reset signals for the field instruments.
d) Indication of instrument fault condition (detector, EHT & LV supplies failure), over range &
e) Overload conditions by up-scale or 4-20 mA. (22.5 mA).
f) Pump failure alarm contact.
g) All these signals will be terminated on 17 pin sockets (Allied Connectors). The corresponding mating plug with 5 mtr cable will be supplied with the monitor. h) RJ 45 connector for Ethernet port.
Computer Interface: The monitor shall have a Ethernet 10/ 100 Mbps port for interfacing with a remote Windows. The features supported by Ethernet port are given below.
The PC and the monitor shall operate in a client-server 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 / receive the instrument data to/from the Host PC on demand.
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.
The firmware is designed for high reliability and availability.
Test points are provided for checking the EHT voltage and for connecting external input pulse signals.
Input Power: 230VAC +/- 10%, 50Hz, single phase supply. Power ON/OFF indication will be provided with an indicator LED. Spike suppressor and line filter are provided.
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
EMI / EMC compliance: As per IEC 61000 / ANSI N42.17