Close

The Compensation Capacitor

A project log for Global radiation monitoring network

The uRADMonitor is a plug-and-play, low power, self contained radiation monitoring device, connected to a centralised server component.

Radu MotisanRadu Motisan 02/18/2015 at 21:490 Comments

Normally, the Geiger tube delivers a sharp short pulse, with an abrupt descending path, as the quenching gas very quickly neutralises the conductive ions, and so terminating the current flow. The uRADMonitor pulses appear with a slightly rounded tip because an extra capacitor is added in the circuit, named the "compensation capacitor". All uRADMonitor model A units have this capacitor:

compensation_capacitor
Here is the original pulse, as recorded on an uRADMonitor model A unit, with the compensation capacitor removed (left picture) and a similar pulse, with the capacitor in place (right picture):
geiger_oscilloscope_compensation_capacitor
The first pulse has an amplitude of 8.48V correctly verifying the resistive voltage formula presented previously, while the second image shows a dampened pulse with a rounded tip and a decreased amplitude that is little over 5V, as an effect of the extra capacitance. Note the voltage divs are different in the two images.

The role of this compensation capacitor has been further explained here: http://www.uradmonitor.com/compensation-capacitor/

Discussions