PicoLog Self-Help Guide
AR346-1
© Copyright 2014 Pico Technology Ltd.
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Incorrect and variable readings are usually caused by a thermocouple touching
something that is at a different potential to the TC-08 or PC earth. If this voltage is
greater than about ±7 V, the channel is pulled out of the common-mode range of the
TC-08. This causes all channels to read very incorrect values. You must ensure that the
metal object you are touching with the exposed end of the thermocouple is earthed
correctly and at the same potential as the PC earth. If that cannot be done, the
thermocouple must be electrically isolated from the metal surface. Failing that, for short-
term logging, you can use a laptop running on batteries, as that is not connected to
mains earth.
The overload can be on one channel, or between channels. The TC08 has an input range
of approx 70 mV. If more than 7 V difference occurs between any of the inputs to the
TC-08, incorrect readings will result. Additionally, if more than 7 V difference occurs
between the TC-08’s ground (also computer ground and usually mains earth) then errors
will occur. A typical example where this may occur is when a thermocouple is used to
measure the temperature of the motor on a machine tool. The casing of the motor,
although earthed, may be at a potential several volts different to that of the earth of the
computer.
Plug in the thermocouples one by one to locate which are causing the problems. If
possible, electrically isolate the thermocouple. If this is not possible, run a wire from the
metal outer shell of the TC-08 USB connector to a point near the thermocouple tip. This
will earth the area near the thermocouple tip and is often enough to pull the two grounds
close enough for normal operation.
Laptops running on mains adaptors can also cause problems. Some laptop power
supplies do not have an earth connection and produce large amounts of interference
which can be picked up by the sensitive TC-08. If you have problems when the laptop is
run off its mains adapter, but not on battery, try earthing the laptop. There is often a
screw on the back of the laptop that can be used for this purpose. Alternatively run a
wire from the TC-08 USB connector shell to mains earth. The USB TC-08 can be modified
to have a 4 mm ground socket if required. Contact Technical Support for further details:
For links to the USB TC-08 Temperature Logger User’s Guide and the USB TC-08 Single
Channel Terminal Board please refer to the Related Documents section in this document.
15.2
Device-specific – PicoLog 1012 and 1216
Sampling at 1 ms in PicoLog with the PicoLog 1012 and 1216
If you find that you any only log at about 20 to 50 ms sampling rates, you are probably
running in "Real Time Continuous" mode.
This mode allows you to use multiple loggers at one time but the sample rate is slow (20
to 50 ms, dependant on PC speed). 1 ms cannot be obtained even if requested.
It does, however, allow you to also plot AC voltage, frequency and dB figures for signals
that are too fast for the logger to capture the actual waveform.