PicoLog Self-Help Guide
AR346-1
© Copyright 2014 Pico Technology Ltd.
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The positive output of the supply goes to the positive terminal of the sensor and the
sensor output terminal loops back to the other end of the 120 Ω resistor. Thus the
sensor current goes round in a loop through the sensor, resistor and supply.
Assuming you have connected up the sensor, resistor and supply as described above,
you just need to set the scaling for the channel in question. Below is an illustration of
how to set-up channel 1 for 4–20 mA operation with graph scaling from 0 bar to 10 bar
as an example:
1.
Start PicoLog and set-up your sample rates as required.
2.
When you get to setting up Channel 1 (ADC-24 Channels), highlight Channel 1
and click Edit.
3.
Type Pressure as the Name, choose a Conversion time between 60 ms and
660 ms, and then select ±2500 mV as the Voltage range.
4.
Leave Differential input enable unchecked.
5.
Now click Options. (You might be asked to save the present setup. Click OK.)
6.
In the Parameter Options dialog box tick Use parameter Formatting, type bar in
the Units box. Field Width = 4, Decimal places = 2, Minimum value = 0,
Maximum value = 40. Now click on Scaling to go to the next dialog.
7.
In the Parameter scaling dialog box, select Table Lookup as the Scaling method
and in the text box, type:-
480 0
2400 10
This tells the program to equate 480 mV to 0 bar on the graph and 2400 mV to
10 bar on the graph.
For your information, the 480 mV is derived from 4 (mA) times 120 (Ω) =
480 mV. The 2400 is 20 (mA) times 120 (Ω) = 2400 mV.
8.
Click OK to go back through the open boxes and channel A should now be scaled
from 0 to 10 bar.
If the sensor is not powered-up, the reading will be about –1.2 bar as that is the
equivalent reading for zero mA. (0 bar = 4 mA).
Look through the PicoLog manual for information on using PicoLog or click on the Help
button at any stage in PicoLog.
Sample rate for ADC-20/24
The ADC-24 will take readings on a single channel at about 1.5 to 17 samples/second,
depending on your requested conversion (settling) time. When setting up each channel,
you are asked to select the conversion time from 60, 100, 180, 340 or 660 ms. For short
settling times, the full resolution of the converter cannot be reached. For 660 ms, the full
resolution is obtained. Please see page 12 of the ADC-20/ADC-24 High_Resolution Data
Loggers User’s Guide (see Related Documents).
The settling time for the ADC-24 is fixed by the hardware and is independent of the
requested sample rate set in PicoLog. If samples are requested faster than the settling
time chosen, then consecutive readings will often be of the same value until the value
for 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 than the settling time, the readings
will always be the latest value that has been taken by the hardware.