PicoLog Self-Help Guide
AR346-1
© Copyright 2014 Pico Technology Ltd.
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30 seconds to decay from 7 A down to under 2 A and the step back up to 7 A takes only
about 5 seconds. The CM3 is not suitable for measuring current transients. The settling
time can be reduced by using current clamps with a higher mV/A rating or looping the
current-carrying cable through the clamp multiple times. The PicoLog software can be
set to scale these readings back to the correct value. The higher the voltage into the
CM3, the faster the settling time will be.
Each CM3 logger takes 720 ms per channel activated, so three channels are read in
2.16 seconds. The currents are measured in sequence, to a regular time pattern, but the
readings are only updated once per cycle, all at the same time. The PicoLog program,
running on the local PC, can only access the data by polling the CM3 on a regular basis.
Normally it requests samples from the logger at a slower rate than the logger cycles
through so that there is always a new reading available. It is possible to set the sample
rate of PicoLog faster than that so it can detect a change in reading with a worst-case
delay of one sample period.
Two or more CM3 loggers can be controlled by PicoLog and data recorded and displayed
together, but the units are not synchronized with respect to sample time. The CM3
loggers are independent so they each log at 2.16-second cycles when three current
clamps are used on each.
Note: The PicoLog CM3 Current Data Logger is suitable only for AC current
measurements. For DC current monitoring, we suggest using a DC current clamp with
one of our PicoScope oscilloscope models.
For a link to the PicoLog CM3 Current Data Logger User's Guide, please refer to the
Related Documents section in this document.
15.6
Device-specific – USB DrDAQ
To be able to use any of the three external sensor inputs as plain voltage channels, you
must have a fixed and defined resistor fitted between pins 2 and 3 of the external socket
to tell the DrDAQ which scaling to use.
The scaling is defined by a Scaling.dds file which you must generate and put in the root
directory of PicoLog. Below is an example file Ext Volts.dds which you can use as a start.
If you put a 3.3 kΩ resistor between pins 2 and 3, that will tell PicoLog to use [Scale1],
which will then give you voltage readings between 0 V and 2.5 V on any Ext Input that is
connected.
