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area gamma monitor [ Type : ga 720]  
Technical Data

Area Gamma monitor Type: GA720, manufactured & supplied by NUCLEONIX SYSTEMS is designed using state-of-art electronic devices (latest) including microcontroller with associated peripheral devices and other discrete ICs & components. Use of these devices makes it compact & highly reliable. Powerful embedded code adds-up and enhances its performance and gives extra advantage from the angle of fault diagnostics, programmable features & measurement of dose rate & data communication under networked environment. This unit is primarily designed to indicate dose rates in the unit selected & produces audio / visual alarms, if the dose rate exceeds preset value. By default the unit is set to be in mR/hr & the range is (0.01-100 mR/hr).

Electronic unit will be useful for monitoring Gamma dose rate levels in working areas of Radio Isotope Laboratories, Radiology departments, Medical & Industrial Radiological installations apart from its usefulness in Atomic Power Stations, radiochemical plants, waste immobilization plants etc.,

With power ON, initialization of hardware, peripheral devices, seven segment LED display, 16x2 LCD display / timers, counter etc, takes place. Followed by this, dose rate calculation takes place in the selected unit such as mR/hr. Additionally, hardware & fault diagnostic check will be carried out. Display updating will take place every 4 sec. Time constant (TC) for doserate will be computed depending upon the detector output count rate.

Area gamma monitor indicates dose rate digitally on 6x7 segment LED display as well a 16x2 LCD display. There are two visual annunciator lamp windows GREEN & RED for NORMAL & ACTIVE conditions respectively. The ACTIVE window flashes once the dose rate alarm occurs and in normal condition the NORMAL window glows.

The user interface is through a front panel keypad comprising of EHT, PROG, INC, DEC, ACK & RESET keys. PROG key shows up different menu options on successive operation. INC, DEC are used to scroll / select various PROG options. ACK and RESET are used for acknowledging and resetting the unit during Active alarm condition. The unit has user selectable options like Alarm preset level, Baud rate (for serial communication), Reset mode (auto or manual) and other system settings. Pressing EHT key displays the current EHT value in the detector probe.

For external detector arrangement, the detector probe can be connected to main Electronic unit by a multicore cable with both end connector arrangement upto a maximum of 30 meters or even more.


  • Performance specifications confirm to ANSI N42.17A.
  • EMI/EMC compliance as per IEC 61000.
  • Structural design seismic qualified confirming to IEEE-344 STD.
  • Microcontroller based design with extensive use of peripheral devices & serial bus interface has been employed.
  • Dose rate range covered is (0.01-100) mR/hr by default, with option of selection of other three 'units' namely µSv/hr, CPS & CPM.
  • Auto ranging & auto TC selection in the range of 30 sec to 0.5 sec depending upon detector count rate.
  • Large size 6x7 segment LED indication for dose rate is provided.
  • Designed using GM tube type GM130E.
  • Large size WINDOWS for NORMAL & ACTIVE alarm condition.
  • 16x2 LCD dot matrix display for visualization & setting of various options.

Radiation to be detected :
X -ray & Gamma Radiation.

Range :
0.00 - 100.00 mR/hr
0 - 1000.0 µSv/hr
0 - 50000 CPM
0 - 2000 CPS
Range and Unit are configurable

Detector : Halogen quenched G. M. Tube. GM131E or Equivalent.

Energy Dependence : Within +/- 18% of true dose rate from 100 keV to 1.33 MeV gamma rays.

Accuracy : +/ - 10% with Cs-137

EHT : 400V to 700V DC adjustable (Typical 500V)

Display : Auto ranging direct reading, 6 digit 7 segment LED display & 16x2 LCD display. 6x7 LED display is interfaced using multiplexed display driver. 6x7 segment display is used for display of dose-rate and hardware status indication & 16x2 LCD for visualization of preset alarm and other parameters.

Display Resolution : 0.01mR/hr / 0.1 µSv/hr / 1 CPS / 1 CPM

Overload : Senses overload above 200% of full scale and upto 10R/h & indicates “OL” on display.

Over-range : Senses if the radiation field being measured has exceeded the measurement range of the instrument above 200% of the higher range and displays “OFl”

Recorder output : 4 to 20 mA, with 600 ohms load.

Time Constant : First reading on Power ON within 5 secs.
Normal (Slow) : 30 sec to 0.5 sec automatically varying inversely with the radiation level (Count rate).
Abrupt detection : Updates the current reading within 2 sec and returns to normal mode.

Calibration Accuracy : +/- 10% through out the range.

Instrument “ON” Indication : RED Neon indicating A.C. lamp

Alarm range : 0.1 - 99.9 mR/hr OR
1 - 999 µSv/hr
0 - 50000 CPM OR
1 - 2000 CPS

The alarm level setting can be set through front panel keypad or RS-485 Serial port using handheld configurator or PC provided with password protection. Front panel keypad is provided with DIP switch de-activation

Alarm Indication :
a) RED (LED) flashing large area window display
b) Loud audio tone (dual frequency tone)

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 (This is inside the cabinet) with Power ON indication

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.

Detector Housing:
a) The G. M. Detector is located external to the Monitor.
b) It is housed in a suitable, air-tight SS shell with built-in pre-amplifier to drive upto 50 mtrs long cable.

Monitor Enclosure:
a) Vapor-tight, rugged & elegant.
b) The door is provided with lock and key arrangement
c) The enclosure is designed to qualify minimum industrial protection Class IP-54.

Mounting: Detector housing is mounted using clamps on top of the monitor. The monitor is wall mountable type. Brackets for the monitor & detector housing are supplied along with the equipment.

Remote /External Console :
a) 4 - 20 mA linear, proportional to full scale display output. Current output will be able to drive load of 600 ohms. (Output circuitry shall 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 gets energized on NORMAL condition and de-energized under ALARM condition.
c) Remote alarm acknowledgement and reset signals for the field instruments (Normally open contact).
d) Indication of instrument fault condition (detector, EHT and LV supplies), over range & overload conditions by up-scale 4-20 mA. (22.5 mA)
e) All these signals are terminated on a 17 pin I/O connector (Allied Connectors). The corresponding mating plug with 5 mtr cable is supplied with the monitor
f) RJ45 connector for Ethernet port
g) RS-485 serial port (optional). This is provided, on a pair of D-type connectors (male & female).

Computer Interface :
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) :
This monitor has a RS-485 Serial Communication port for interfacing with a PC. The PC and the monitor 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 the various functions as per the required information in response to the queries.

The firmware of the monitor sends 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 receives commands from Host PC and carries 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 are password protected and the password is user defined.

The detailed specifications for the interface are as follows:-

Type : RS-485 Multi-drop Serial Communication Port, Half Duplex Bi-directional communication.
Character Format : ASCII
Protocol : Modbus/RTU
Bit Rate : User configurable to 9600 or 19200 bits per sec.
Address : User configurable from 0 to 255.
Connector : 9-pin D-type connectors (2 connectors connected in parallel for daisy chaining a number of instruments). The mating connectors with cover are supplied.

Self Diagnostics : The monitor has built-in self diagnostics. On being powered it performs tests to ensure that all components and sub-systems are functioning properly. It checks for the Power supply, High Voltage Supply, Detector and pulse processing electronics.

Input Power : 230VAC +/-10%, 50Hz, single phase supply. Power ON/OFF switch is provided with a neon indicator. Spike suppressor and line filter are also provided.

Environment : This instrument can withstand temperature upto 50o 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 are IP-54 compliant.. Electronic unit will withstand cumulative radiation dose of 10000 Rad. (30 years of operation).

Seismic qualification : Electronic unit, its wall mounting bracket, detector probe, wall mounting clamp and floor mounting stand are seismic qualified confirming to IEEE-344

EMI / EMC compliance : As per IEC 61000 / ANSI N42.17

Mechanical Enclosure :
Size : 357H x 380W x 140D,
Weight : 8.5kg approx

Options :
(1) 16 bit resolution current loop (4-20mA) instead of 14 bit resolution.
(2) Log scale O/P for 4-20mA instead of 4-20 linear O/P
(3) 3.5” QVGA color TFT display in lieu of 7 segment LED & 16x2 LCD display
(4) RS485 serial interface
Plot No.162 A & B, Phase-II, IDA, Cherlapally, Hyderabad-500051 India Phone: +91-7207034546, +91-7331104481, 7331104482, Fax : 040 - 29706486.
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