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 The CHECKMATE™ daily output constancy meter is simple, basic and fast. Outfitted with a single ion chamber, the instrument is designed to perform fast and efficient central axis measurements.
Large, 2 cm high, LED characters display each measured value. The results are visible from a closed circuit monitor. The instrument automatically resets for the next exposure and performs air-density corrections.. The CHECKMATE™ is self-contained, even down to its fully battery-powered operation. There are no cables to connect, and no computer to operate as an interface.
Detector
- Type: Vented Ionization Chamber, Fully Guarded
- Quantity: 1, located for CAX measurements
- Volume: 0.6 cm3
- Parallel Plate Separation: 4 mm
- Detector Bias: 400 volts
- Collection Electrode: 1.4 cm dia, carbon
- Inherent Buildup: Actual; Acrylic, 0.79 cm; Mylar, 0.038 cm, Effective; 1.0 ± 0.1 g/cm2
- Inherent Backscatter: Acrylic, 2.3 cm
- Radiation Measured: Photons: Co-60 to 25 MV, Electrons: 5 MeV to 25 MeV
- Beam Limits: Maximum dose per pulse, 0.055 Gy, maximum average dose rate, 0.63 Gy/s
Construction
- Single circuit board for high reliability, mounted between acrylic plates, providing a high quality EMI shield. Electronics placed at display end must be kept out of direct radiation.
- Top covered with durable alignment template
- Dimensions: 25.5 cm W x 40 cm L x 4.7 cm T
- Weight: 4.9 kg
Alignment Template
- Light Field Alignment: 10 x 10, 20 x 20 cm square
- Tolerance Marks: ± 2 mm at the light field corners
- Detector: Located by blue circle
- Cross Hair Intersection: 2 mm diameter circle within the blue detector area.
Calibration
- 15 memory locations provide correction factors which calibrates the display to read 15 different beams. After calibration the display is in units of % of the stored standard value.
Software Functions
- Automatic leakage offset compensation
- Automatic measurement reset
- Automatic air density correction
- Displays measurement as percentage of standard value
- Manual or automatic selection of standard output memory locations
- Battery monitoring and status indication
- Standard outputs for fifteen beam conditions
Power Supply
- Rechargeable gel-cell batteries: 4.0 volts (nominal)
- Battery Charger: AC/DC adapter (110 VAC 50/60 Hz included), 6-12 VDC (damage will occur above 16 V), Center positive, greater than 300 milliwatt
End Panel
- 4 Digit LED display: 2 cm high
- DC input power jack: 2.5 mm diameter center pin
- Power switch: On/Off, labeled (1/0)
- Indicators: 3 green indicators
- “CHARGING” - Battery charging
- “STATUS” - Battery status: Full = off, 20-80% = solid on, <20% = rapid blink
- “ON” - Power on and processor operational
• Controls:
“CALIBRATION” - Pushbutton switch saves a measurement as a standard in the selected memory
“*” - Pushbutton switch toggles auto mode for memory selection with radiation measurement
“SELECT” - Pushbutton switch manually selects memory location for calibration or measurement
“DISP.” - Potentiometer adjust of display brightness
• Test Points:
“G” - Ground
“B” - Battery voltage (3.50 - 4.59 volts, operational range)
“C” - Charger voltage (0.05 - 4.59 volts), Charging current = [(C-B)/0.1]
Instrument Firmware
- Execution: EPROM located in microprocessor
- Update: Requires new microprocessor
Measurement Electronics
- Detector Measurement: Unipolar current to frequency
Mos-FET operational amplifier
Maximum pulse frequency, 20,000 Hz
Charge per pulse, 2.5 pC
Feedback capacitor, 220 pF
Amplifier supply voltage, 5V
Update Frequency, 1 second
- Capacitor Reset: Pulse charge feedback
- Single Gain
Temperature and Pressure Correction
The CHECKMATE employs internal temperature and pressure sensors. With the information from these sensors the CHECKMATE performs automatic air density correction of all measurements.
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