Logarithmic Meters:

Radiation detection circuit currents or pulse rates vary over a huge range of values. A current  outcome  of  an  ionization chamber might vary through 8 sequences of magnitude. For instance, the range might be from 10-13 amps to 10-5 amps. The most accurate method to show this range would be to utilize a linear current meter with various scales, and the capability to switch those scales. This is not practical. A one scale that covers the entire range of values is used. That scale is referred to as logarithmic.

The logarithmic outcome meter has to be given along with a signal that is proportional to the logarithm of the input signal. This is simply completed through using a diode while the input signal is from an ionization chamber. A voltage across the diode equals the logarithm of the current by the diode. Through using this principle, the simplified circuit, displays in Figure, is used to convert  ionization chamber current to a voltage proportional to the logarithm of this current.

Figure: Log Count Rate Meter