PicoLog Self-Help Guide
AR346-1
© Copyright 2014 Pico Technology Ltd.
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channel terminal board. Connect the 0 V of the power supply to the Com terminal of the
single-channel terminal board. Set the switch of the single-channel terminal board to
4-20 mA.
The text below explains the setup process:-
The 4-20 mA will flow through a load resistor on the adapter board, generating between
9.5 mV (@ 4 mA) and 47.5 mV (20 mA). To convert these voltages into properly scaled
readings, you must use the Scaling option in PicoLog.
For example, if the sensor pressure is 0 psi when the current through the load resistor is
4 mA and 30 psi at 20 mA, you would set up a lookup table to equate 9.5 (mV) to 0 (psi)
and 47.5 (mV) to 30 (psi).
1. Start PicoLog and set-up your sample rates as required. When you get to setting up
channel 1 (Edit TC-08 channel), type psi as the Name and mV as the thermocouple.
2. Now click on Options.
3. In the Parameter options box, tick Use Parameter Formatting and set Units to psi,
Formatting to your own preference (three digits, one after the decimal point?), select 0
(min) and 30 (max) for the graph scaling and then click Scaling.
4. In the Parameter Scaling box, set Scaling method to Table look-up.
5. In the blank box, you can now enter two pairs of Raw and Scaled readings. In this
case the table looks like:-
9.5 0
47.5 30
(Note the space between the two numbers on each line.)
The 9.5 is derived from 4 (mA) times 240 (Ω) divided by 101 (attenuation in the single
channel board) = 9.5 mV.
The 47.5 is 20 (mA) times 240 (Ω) divided by 101 = 47.5 mV.
6. Click OK to go back through the open boxes and channel 1 should now be scaled from
0 to 30 psi.
Click on Help for an explanation of the process.
TC-08 channels all showing incorrect and variable readings
The 8 channels of the TC-08 are differential inputs. There are two pins per channel, each
with a 1 MΩ resistance to ground. The differential input resistance is thus 2 MΩ. The TC-
08 measures the difference in voltage between the two pins with a working range of
±70 mV maximum. For correct operation, both input voltages must stay in the range
±7.0 V with respect to ground (0 V). No damage will result if this common-mode voltage
is higher than ±7.0 V unless the voltage increases to above ±30 V. As long as all the
voltages stay within ±7.0 V of 0 V, the channels will read correctly.
