Two basic types are analog and digital. The digital Geiger counter is typically more accurate as you can obtain an exact count of radioactive particles detected. Where as the analog meters average out reading, and do not provide a display for the detected particle count. A digital readout from the GCA-06W is shown in figure 8 below.
While many Geiger counter manufacturers claim high accuracy for their Geiger counter, it simply is not true.
It is not enough to say an instrument is calibrated, or has an accuracy of 1%, 5%, 10%, or 20% because without a legitimate standard calibration reference, a claim of accuracy is meaningless.
Fortunately, there is a government approved Geiger Counter calibration standard, it is the ANSI-STD N323A. Passing this calibration standard certifies the accuracy of your Geiger counter instrument. The ANSI-STD N323A calibration should only be performed by a government licensed nuclear laboratory conforming to the Nuclear Regulatory Commission (NRC) regulations 10-CFR-34 and 10-CFR-35.
Without passing the ANSI-STD N323A calibration by a licensed lab, you cannot be sure of any claim that a Geiger counter accuracy is valid. Below is a picture of a calibration label for one of our Digital Geiger Counters. After passing ANSI-STD N323A calibration, a certification label is attached to the Geiger counter and this certification is valid for one full year.
When you purchase an NRC Certified Geiger counters from Images SI Inc., your Geiger counter has passed ANSI-STD N323A calibration using an NIST traceable source from licensed laboratory conforming to NRC regulations 10-CFR-34, 10-CFR-35.
Before you buy, ask if their Geiger Counter is ANSI-STD N323A calibrated using a NIST traceable source? If not, their Geiger counter probably can not pass ANSI-STD N323A calibration using an NIST source from an independent lab conforming to NRC regulations 10-CFR-34, 10-CFR-35. But if a seller claims the ANSI-STD N323A calibration is expensive and is not necessary. Ask, "If I send your Geiger counter for calibration to ANSI-STD N323A standards using a NIST traceable source will it pass? And more importantly, if it fails calibration, can I return the Geiger Counter for a full refund?" The seller's answer will tell you what you need to know to make a sound purchasing decision.
Without this ANSI N323A calibration, there is no reference point, to make a claim that the Geiger Counter accuracy is valid.
Below figure 9 is a picture of a Calibration certification label for the GCA-07W
* All digital Geiger counters sold by Images SI Inc. can be NRC certified to their accuracy.
Where to Obtain ANSI N323A Calibration:
There are a number of independent laboratories that are licensed by the U.S. Government to test Geiger counters for their accuracy, and if it is accurate provide an Calibration certification label attached the Geiger Counter. The certification is good for one-year.
The laboratory my company uses is:
Applied Health Physics Inc.
2986 Industrial Blvd.
Bethel Park, PA 15102