Trade.Information

Product Name: G64 Gamma Monitor

Product Description

For remote monitoring applications, the detector assembly can be easily decoupled and installed at distances of up to 100 meters from the Display/Alarm unit. A Remote Detector Kit is required, if the detector is to be used remotely. The user must simply ensure that connections between the detector and the main electronics unit are correct and that the detector is suitably mounted.

The G64 is also available with an optional ion chamber detector module for high range applications.

Features
Solid state detector with wide dynamic ranges
Removable detector for remote use
Ion chamber detector option for high range applications
Three user-set alarm levels across the full range
Local signaling by relays or communication outputs
Displays on analog meter and LCD
Status, fault, and alarm messages shown clearly
Membrane pushbuttons allow alarm reset
Internal keypad allows adjustment and calibration
Interlock monitor option

Operating Principle

A block diagram of the G64 with solid state detector is shown in Figure 1. 

Gamma radiation interaction in the G64 solid state detector deposits units of charge whose magnitude and frequency are proportional to the incident energy and dose rate. These charge pulses are amplified and shaped to produce a series of voltage pulses, each of which, if it is above the minimum energy that the G64 has been designed to detect, trigger’s an RS-422 pulse which is sent to a scaler. The scaler contents are read out at regular intervals by a microprocessor and converted to the corresponding radiation dose rate. An adaptive software algorithm is used to ensure both a rapid response to step changes and good statistical accuracy, even at low dose rate levels. The microprocessor controls the G64’s indicators, alarm annunciators and external communications.

Although many operating parameters are fixed, the user has the option to configure certain parameters to specific applications via an internal keypad.

Calibration
The G64 can be calibrated automatically using a suitable gamma source emitting a known dose rate. The user is prompted to enter the dose rate of the source and the counting time over which the calibration is to be made. The G64 will display the counts acquired during this period. On the basis of this result, the user may retain the current calibration factor or request the instrument to calculate a new factor, which is then stored.

Configuration
The G64 incorporates a universal power supply that operates over the mains range of 85–264 V ac. Therefore, no switches or links are required to operate at any voltage within this range. On power-up, the G64 will perform a self-test and when this has been successfully completed it will commence monitoring.

he precise mode of operation can be set or adjusted by the user via the internal keypad, accessed by unscrewing the four retaining screws and opening the hinged front panel. Password protection is provided to ensure that only authorized personnel can adjust the configurable operating parameters, which include:
Alarm levels and responses
Fault condition responses
Alarm level detection factor
Communications mode (RS-232 or RS-485)
Analog output (0–1 mA or 4–20 mA) and range (number of decades)
Detector calibration factor.

Once the G64 has been configured, the front panel of the Display/Alarm unit is closed. Thereafter, the status of the operating parameters may be viewed, but not changed, by means of membrane keys on the front panel.

In the event of an alarm situation, two membrane keys are accessible on the front panel to allow the user to mute the sounder (the beacon continues to flash) or to reset the instrument.

To remove the detector assembly, simply open the front panel of the G64, pull out the retaining pin and unplug the assembly from the top of the unit (see Figure 3). Install and connect the detector using a G64 Remote Detector Kit, which consists of:
Detector mounting bracket
Cover plate for top of main G64 unit
Cable (standard lengths 10 m, 25 m or 100 m), terminated with a 9-way D-type connector that plugs directly into the remote detector.

The flying lead of the cable is connected to the screw terminal block within the instrument. The cable is a twin twisted-pair; two wires for dc power and two for RS-422 pulses from the detector.

Indicators
Two displays indicate the dose rate:
A moving coil analog meter with a 6-decade log scale, which can be viewed from a distance
A 16 character x 2 line liquid crystal display (LCD) provides more precise indication of the dose rate. It is permanently backlit for easy viewing.

Alarms and Annunciators
The G64 has three alarm thresholds, all of which are user-settable. The “alert” and “high” alarms are triggered when the ambient radiation level exceeds these thresholds. Both can be set across the range of the instrument, although the alert level must always be less than the high level. The user can select which annunciators are associated with these alarms, whether they are to be latched or unlatched, and what detection factor is to be applied.

The detection factor allows the user to set thresholds at a fixed number of standard deviations above and below each alarm level to provide confidence that an alarm is genuine, rather than a statistical fluctuation. For example, if an alarm level is equivalent to 100 cps recorded in the detector and the detection factor is set to 2 sigma, then the alarm will be generated when the count rate exceeds 120 cps and will be maintained until it falls below 80 cps.

The low alarm threshold differs from the other two in that, in this case, the alarm is triggered if the radiation falls below this level. Its main purpose is to identify a detector failure and it, therefore, shares the same relay as the equipment fault.

Alarm annunciation is by means of:
The red beacon, which flashes
The sounder, which can be configured by the user to one of 24 different tones and frequencies (e.g., to avoid confusion with other plant devices) via switches accessible behind the internal keypad.

LEDs, located below the LCD, indicate which of the three alarm conditions has been registered. The user may suppress alarm annunciation for either or both of the activity alarms if required.

In the event of a sustained mains failure, dose rate measurement is suspended but the annunciators are supported by an internal battery for up to 15 minutes.

Outputs and Communications
Connections to the G64 are via a screw terminal block, accessible, with the front panel open, through glands on the underside of the instrument (see Figure 6). The G64 enables the user to control external devices and to transmit data to local or remote locations via:
Three sets of volt-free changeover contacts for the alert and high activity alarms and the low activity alarm/equipment fault condition (all relays operate in the fail-safe mode, i.e., normally energized)
RS-232 serial port for communicating data to a PC or printer
RS-485 serial port for communication with remote monitoring systems
Current loop output for driving a chart recorder
RS-422 pulse output for connection to distributed control systems.

The G64 incorporates a number of hardware and software diagnostics to identify the nature of any fault in the operation of the instrument. Faults that will be detected are:
Red or green lamp failure
5 V, 12 V or 24 V dc line fault
Low internal battery voltage
Detector fault
Mains failure
Microprocessor fault.

Occurrence of any of these conditions will cause the green beacon to flash and will fire the “equipment fault” relay. The nature of the fault will be displayed on the LCD.

The G64 includes a back-up battery to provide up to five seconds of immunity to temporary mains interruptions and up to 15 minutes preservation of fault indicators if the interruption is sustained. During this period it will emit a constant audio tone and flashing green beacon and the “AC fail” LED will be illuminated.

Ion Chamber Detector Module

The G64 Ion Chamber Detector Module is a small, environmentally protected gamma radiation detector, to replace the standard solid state semi-conductor detector in high dose environments. The ion chamber detector module comprises two items, the detector and a separate amplifier. The detector module can be connected to the amplifier by up to 10 m of special connecting cable (supplied). The amplifier is connected to the G64 through up to 100 m of twisted-pair cable (screened). It is powered from the G64 and provides an output signal as a variable frequency pulse at RS-422 interface levels.

G64 Interlock Monitor
The G64 Interlock Monitor is identical to the G64 Area Gamma Monitor previously described except for:
The flashing beacon is not fitted
The audible alarm sounds only in the event of an equipment fault.

The three sets of volts-free changeover contacts provided in the monitor can be configured for interlock control. The G64 Interlock Monitor can be supplied with the standard solid state detector (fitted to the instrument or mounted remotely) or with an ion chamber detector for applications in which the detector will be used in high dose environments.

D1 Slave Alarm

The D1 Slave Alarm (see Figure 8) is designed for use with any monitoring instrument, including the G64 Area Gamma Monitor, whose output provides a pair of volt-free relay contacts. In its standard configuration the Slave Alarm is actuated when the relay contacts open, signaling the alarm condition with an audio sounder and a flashing red beacon. The D1 is mains powered and can be set for use with a 110 V or 240 V ac power supply, and to alarm on opening or closing of the relay contacts.

Related Equipment
CANBERRA-Harwells' PC-based Environmental Monitoring System (PCEMS) is a system for networking area radiation monitors and other non-radiological plant instruments.

Accessories
Remote Detector Kits via 4-way cable (10 m, 25 m, 100 m)
Stand
Test pulse generator.

Company Details

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