The ELECTRA/SELECTRA Ratemeter is a portable instrument designed for measuring radioactive contamination and radiation using various GM and Scintillation probes. The SELECTRA model is specifically designed for use with Thermo Electron's "intelligent" GM and Scintillation "I" series probes.
Function Description:
The ELECTRA/SELECTRA Ratemeter measures radioactive contamination and radiation. When an "I" series probe is connected to the SELECTRA, the instrument automatically interrogates the probe's on-board memory to retrieve and apply its operating parameters. This feature allows for immediate monitoring without manual setup adjustments. The SELECTRA is designed for high accuracy in lower level discriminator and high voltage settings, ensuring consistent performance across different SELECTRA units and facilitating the interchangeability of "I" series probes without performance variation.
The instrument can operate in two main modes: rate measurement and integrate mode. The rate measurement mode provides a continuous display of the current radiation level. The integrate mode allows for more accurate measurements over a presettable time, with a background subtraction facility that can be activated or deactivated. For dual scintillation probes, the instrument can simultaneously monitor alpha and beta contamination, providing separate audible tones and independent alarm levels for each particle type. The display can be configured to show either alpha, beta, or the sum of both. For gamma scintillation probes, an energy selection facility with an adjustable upper threshold is available. In GM settings, the instrument performs an integrated dose measurement, which can be viewed during most operations.
Important Technical Specifications:
- Power Supply: The unit is powered by three standard 'C' size cells. It supports both primary (alkaline manganese, IEC LR14) and rechargeable (IEC KRH 27/50) cells. Rechargeable cells can be recharged within the unit using an optional mains operated charger, which also functions as a DC supply.
- Power Supply Adaptor: Output 5 V ± 0.25 V DC, maximum current 250 mA (for battery charging). Only approved power supply adaptors from the list in section 3.8 should be used, and they should not deliver more than 250 mA DC current.
- High Voltage: Up to 1400 V (maximum power 45 mW) at the probe connector.
- Display: High contrast LCD with both analogue (logarithmic bargraph covering three decades with autoranging) and digital formats. Auto-ranging display capable of showing Counts per second (cps), Counts per minute (cpm), Becquerel (Bq), disintegrations per minute (dpm), Bq/cm² for contamination, or sieverts per hour (Sv/h), roentgens per hour (R/h), or grays per hour (Gy/h) for doserate measurements.
- Backlight: Available for low light conditions, activated by a front panel key.
- Audible Output: Internal sounder for audible indication of measured rate and an external headphone socket. Volume control is available via a potentiometer under the outer end cap.
- Alarms: Presettable alarm levels with continuous tone and display indication when exceeded. Alarms can be disabled.
- Memory: Battery backup maintains all entered parameters and alarm levels even when batteries are removed. The instrument prevents rate measurement if parameters are corrupted due to backup battery failure.
- Probe Connectors: ELECTRA1A is fitted with a PET probe connector, while ELECTRA1B is fitted with an MHV connector.
- EMC Compliance (for EC users): Instruments manufactured after 1.1.96 comply with EC EMC Directive 89/336/EEC (amended by 92/31/EEC & 93/68/EEC) and bear the CE mark. To maintain compliance, only adequately screened cables (Thermo 'curly' cables 3190A - 3192A, 3201A & 3203A may not offer adequate screening) should be used. The instrument should be operated with batteries in harsh r.f. environments; otherwise, only Thermo Electron approved DC Adaptors with a ferrite tube should be used. CE marked Selectra instruments should only be used with Intelligent Probes having adequately screened cables (Thermo Type 3212, less than 3 meters in length). Connecting probes with integral cables may render the Selectra non-EMC compliant. AP6A, BP17A, and DP8A probes require modification (MOD. record 1 on serial number label) for use with CE marked Delta5 instruments.
Usage Features:
- User Interface: Membrane keypad on the top panel with embossed keys for tactile feedback. Audible feedback confirms key presses.
- Quick Operation Guide:
- Switch-on: Press "ON/OFF" to enter Ratemeter Mode.
- Rate to Integrate: Press "RATE/INTEG" to switch to Integrate Mode.
- View Elapsed Time (Integrate Mode): Press "SETUP" to toggle between elapsed time and integrate count.
- Stop Integration: Press "RATE/INTEG" to view the final result.
- Integrate to Rate: Press "RATE/INTEG" to return to Ratemeter Mode.
- Modify Parameters: Press "SETUP" to access the Parameter List. Use the arrow keys to find the desired parameter, press "ENTER" to enter edit mode (parameter flashes), use arrow keys to select the new value, press "ENTER" to register the new value, and finally press "SETUP" to apply changes and return to Ratemeter Mode.
- Store Background: Press "ENTER" in ratemeter mode to store the background.
- Sound Control: Press the speaker icon to toggle sound on/off or temporarily mute alarm sound during integration.
- Channel View: Press "α/β" to change display and sound from alpha to beta to alpha + beta, or to display integrated dose for Geiger probes.
- Backlight: One press gives 30 seconds of backlight; three quick presses provide continuous operation.
- Inhibit Parameters: A feature to inhibit changes to parameters within the parameter list view.
- Switch-off: Press "ON/OFF" to turn the unit off.
- Probe Calibration: The instrument supports probe calibration.
- Probe Interchangeability (SELECTRA only): The SELECTRA automatically configures itself when an "I" series probe is connected, reading operating parameters from the probe's on-board memory.
- Test Mode: Provided to assist customer testing and fault diagnosis, with error messages displayed during normal use.
Maintenance Features:
- Cleaning Instructions: Details are provided in section 7.1 of the manual.
- Internal Switches S1: Unauthorised adjustment of setup parameters can be prevented by selecting an internal switch located under the end cap of the unit.
- Potentiometers: An internal potentiometer is available for volume control of the audible output, situated under the outer end cap.
- Service: The HV/Amplifier Board poses a risk of hazardous electric shock. Servicing should only be attempted by qualified, approved service personnel. Details are contained in the Service Manual.
- Battery Safety: Do not recharge non-rechargeable, primary, alkaline manganese cells. When using these cells, ensure the end cap covers the DC INPUT jack. Insert batteries with correct polarity.
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