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GCA-07W Introduction and Usage

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The model GCA-07 has an internal Geiger Mueller tube. The model GCA-07W uses an external wand that houses the Geiger Mueller tube.

Scientific Instrument & Industrial Tool

Our Digital Geiger counters have been calibrated and certified accurate in reading radiation levels to within 5% from background radiation to 1000 mR/hr. NRC Certification available at additional cost.

Perfect for schools and industry. In the laboratory the Digital Geiger Counter may be used to conduct nuclear experiments and measurements. Free Windows 7 graphing programs. Graphic Files may be exported to Excel spreadsheets.

Communication specifications are provided for users to read the output of the Geiger Counter and write their own programs.


* Education - Classroom demonstrations and experiments
* Emergency Services and Domestic Preparedness
* HAZMAT and Compliance Verification
* Dirty Bomb Screening and EMT's

gca-07w three quarter view


Radiation Detected
Alpha, Beta, Gamma and X-Rays.

Geiger-Muller tube Ne + Halogen filled with a .38" effective diameter 1.5-2.0 mg/cm2 mica end window.

Detector Sensitivity
· Alpha above 3.0 MeV
· Beta above 50 KeV
· Gamma above 7 KeV

Countable Pulse Range 1 (CPM) - 10000 + counts per second (CPS)
Converted Radiation Range .05 mR/hr - 1000 mR/hr (Imperial)
.0005 mSv/hr - 10.0 mSv/hr (SI Metric)

The Liquid Crystal Display (LCD) is 16 character by 2 line that provides an easy to read output, see image to right. LCD has an on-off backlight switch . LCD display continuously updates counts per second (or counts per minute) on line one while displaying converted radiation level second line.

Backlight Switch turns on and off the LCD backlight,.

The LED marked Low Battery will turn on when the battery power drops to approximately 7 Volts to alert the user to change battery. Readings taken when low battery indicator is on may not be accurate.

The LED marked Pulse—is a secondary radioactive particle indicator it blinks each time a radioactive particle is detected by the Geiger Counter.

The Power Switch turns power on or off to the GCA-07.

The Speaker Switch turns the sound on or off to the internal speaker. The speaker is a secondary radioactive particle indicator. It clicks each time a radioactive particle is detected. Note: Plugging a headphone in the headphone jack will automatically turn off the internal speaker.

Headphone jack is a standard 3.5mm for private listening. Using a headphone automatically turns off the internal speaker of the Geiger counter.

External power jack is available for extended readings where battery operation may not be practical. Power jack is 2.5mm x 5.5mm. Power input is 9VDC or 9VAC @ 200mA min. current. Mobile operation uses a 9V battery.

TTL Serial output for PC available via 3.5MM stereo connector. Both the GCA-07 and GCA-07W output the counts per second.

Main Panel Controls

The first panel switch starting from the left selects whether the radiation levels are shown in Systems International (SI) metric (mSv/hr) or imperial (mR/hr) measurements.

front panel gca-07w

The middle switch labeled CPS, AVG CPS and CPM selects one of the three Survey Meter Modes:
CPS Counts Per Second

CPS (Counts Per Second) is a one second counting mode. Real time radiation readings and displays the count/second and equivalent radiation level in either mR/hr or mSv/hr.

3 second average

AVG CPS is a three second average of the CPS. AVG CPS performs a smoothing function similar to analog meter readings. Displays the 3 Second CPS and equivalent radiation level in either mR/hr or mSv/hr.

CPM Counts Per Minute
CPM (Counts Per Minute) is a one minute counting mode for measuring low levels of radioactivity and background radiation: Displays accumulated count and equivalent background radiation in either uR/hr or uSv/hr. If radiation level is significant radiation level is displayed either mR/hr or mSv/hr.


2. Operations

Survey Meter Modes

CPS Mode: Set the Conversion switch to mR/hr (milliroentgen/hour). The time function switch to “CPS”, Backlight switch on and the audio switch on. Turn on the Geiger counter. If you have a radioactive source bring the source close to the GM tube. For Geiger counters with an external wand, bring the wand close to the radioactive source.

CPS Counts Per Second with Text


Every radioactive particle detected will cause the Geiger counter to click and the LED to blink. The LCD digital display in this mode updates the count and radiation level every second, see photo above. The display always shows the previous seconds count and radiation level. The count “Count/Sec” is the number of radioactive particles detected in the previous second. On the second line the equivalent radiation level of that count in mR/hr. You can change the Conversion switch to mSv/hr to read the radiation level in milli-sieverts/hour. 3-Second Average: The three second average of the CPS. AVG CPS performs a smoothing function similar to analog meter readings. Displays the 3 Second CPS and equivalent radiation level in either mR/hr or mSv/hr.


3 second average with text


CPM mode: Displays the counts per minute and convert the radiation level into micro-Roentgens (uR/hr) or micro-Sieverts (uSv/hr). The CPM modes is useful for checking background radiation. First set the switch to Metric or Imperial measurement. Next set the time function switch to CPM. The LCD display changes. The left side of the first line begins a count up to 60 seconds, increasing by 1 each second.


CPM readout with text


The right hand side of the first line displays the number of radioactive particles detected.

At the end of the CPM count the Digital Geiger counter will display the total CPM and equivalent radiation level for one second before beginning another CPM counting cycle.

If you changed to the 1 minute time from 1 second the second line will display the radiation level last calculated from the previous mode. If the Geiger counter is turned on in the 1 minute mode the second line will display the word “Initializing” for the first 60 seconds.


cpm update with count