Using the Griffin Rate Meter with DrDAQ

Introduction

This application note shows how it is possible to interface 'third party' sensors to the DrDAQ data logger. The advantage for schools is obvious, you can re-use many of the sensors you already own.

The Griffin rate meter is capable of counting up to 1999 counts per second with an accuracy of 5%, making it ideal for use in basic investigations into radioactivity. Both an audible and a voltage signal provide indication of the level of radioactivity from a source.

To make quantitative readings the voltage output of the rate meter needs to be connected to a voltage input on the data logger, a change of 100mV in the output voltage will then represent a change of 100 counts per second.

Normally when connecting up such sensors to DrDAQ, the best approach is to use the 0 to 5V voltage input (screw terminals), unfortunately this is not possible for the Griffin rate meter as it requires the data logger to have a very high input impedance (>10 M ohms). The 0 to 5V input on DrDAQ only has a input impedance of 0 to 5V so is not suitable. For this reason we chose to use the pH input (which has a input impedance of over 100 M ohm) and use a software scaling file to convert the input to read counts per second.

Setting up DrDAQ with the Griffin Rate Meter

Follow these steps to set up DrDAQ for use with the Griffin Rate Meter

Put the file griffin.dds in the C:\PICO directory, after downloading and extracting it from griffin.zip.
Connect the Griffin Rate Meter to the DrDAQ pH probe input. This will require a BNC to 4mm plug converter cable (MI029).
Run the PicoLog Recorder software and select File¦New Settings from the toolbar menu.
Enter the required parameters in the 'Sampling Rate' window.
Enter the correct converter type and port information in the 'Converter details' window and then click on the 'OK' button.
Click on the 'ADD' button in the 'DrDAQ measurement indow'.
In the 'Edit DrDAQ Measurement' window select 'pH' for the Channel and select 'Griffin Rate Meter' for the scaling method, then click 'OK'.
Finally click on the 'OK' button in the 'DrDAQ measurement window'.

DrDAQ is now set up to be used with the Griffin Rate Meter.

figure1: The Griffin rate meter connected to DrDAQ.

Figure 2 shows the readings from an analogue watch with a fluorescent 'glow in the dark' face. The first 10 seconds show the background count of ~1 count per second, then the watch was placed in front of the rate meter this is shown by the increase in the readings to between 8.9 & 22.9 counts per second.