PicoLog Self-Help Guide
AR346-1
© Copyright 2014 Pico Technology Ltd.
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You can use the current version of PicoLog (R5.23.0 at the moment). When installing,
still select Serial TC-08 as the device, not USB TC-08.
TC-08 sample rate
The TC-08 takes 100 ms per thermocouple to read temperature, and once per cycle
through all the active channels it must read the cold junction temperature as well, which
takes another 100 ms. Thus, if only one thermocouple is active, the full cycle takes
100 + 100 = 200 ms or 5 readings per second. If two channels are active, the full cycle
takes 2 x 100 + 100 = 300 ms or about three readings per channel per second.
If all 8 channels are in use, the cycle is 8 x 100 + 100 = 900 ms which means all 8
channels are read just quicker than once per second. When the cold junction is being
read (once per cycle) the LED is green. It is red when any of the thermocouple channels
are being read.
The above cycle is constant for the TC-08 and independent of the requested sample rate.
If samples are requested faster than 100 ms, consecutive readings will often be of the
same value until that channel has been updated, so readings are never older than the
sample time at worst. If the samples are requested at a slower rate, the readings will
always be the latest value which has been taken by the hardware no more than 200 ms
ago.
If Filtering is enabled, with say a filter factor of 3, then the display is not updated until 3
samples are available and then the average of those three samples is the value
displayed. It is generally best to set the sample rate to about the same as the cycle time
to get readings from all enabled channels. Adding a filter factor will smooth out
fluctuations in the readings at the expense of slower response to a fast temperature
change.
Using Scaling to adjust the calibration of each channel
Each channel can be adjusted to compensate for calibration errors.
It is easy to add a calibration factor to each channel using the Scaling option during
setup. The corrections can be saved to a settings (.pls) file, allowing the calibration data
to be reapplied to each channel on startup without the need to type everything again. A
greater number of points will give you a better calibration. You can use them to set up
Scaling to give you accurate readings directly to your data file and graphical display.
You just need to set the scaling for the channel in question. We will illustrate how to
scale Temperature for each channel.
Start PicoLog and set up your sample rates as required. When you get to setting up each
channel, click on Edit, then click on Options.
In the Parameter Options dialog box, click on Scaling to go to the next dialog.
In the Parameter scaling dialog box, select Table Lookup as the Scaling method.
