Temperature sensor question

Post all DrDAQ questions here
Post Reply
Hominid
Newbie
Posts: 0
Joined: Thu Jun 28, 2018 6:13 pm

Temperature sensor question

Post by Hominid » Thu Jun 28, 2018 6:35 pm

Hi all - I'm new here, and have a quick question for which I can't seem to find an answer for... I'm looking for a temperature sensor the the DRDAQ that has a lower range than the DD100. Preferably -50C, as I have found some on digikey.ca, but have no idea what resistance range the DRDAQ needs.

It's for a project I'm working on to measure outdoor air temps, and I live in Canada, so the DD100's low end of -10 doesn't quite do it during winter.

Thanks in advance!

Gerry
PICO STAFF
PICO STAFF
Posts: 323
Joined: Mon Aug 11, 2014 11:14 am

Re: Temperature sensor question

Post by Gerry » Fri Jun 29, 2018 2:19 pm

Hi Hominid,

You need to search for a 100kΩ NTC thermistor with a low enough temperature range,to give you a range of options, e.g. https://eu.mouser.com/Circuit-Protectio ... m4Z1z0z7l5.

Once you have the thermistor you can then connect it across pins 1 and 2 of the Ext 1, 2 or 3 inputs of the DrDaq, (the Input has a 100K pull-up resistor to 2.5V so you can use the thermistor in a potential divider), and then get a temperature versus resistance curve from the manufacturer/supplier. You can then use the values from the temp Vs Ω curve to create a scaling file that you can apply to the input channel of the DrDaq using our PicoLog software, to log the data as Temperature (see page 121 of the PicoLof 5 Users Guide here: https://www.picotech.com/download/manua ... sGuide.pdf, which is also supported in PicoLog 6).

Regards,

Gerry
Gerry
Technical Specialist

Hominid
Newbie
Posts: 0
Joined: Thu Jun 28, 2018 6:13 pm

Re: Temperature sensor question

Post by Hominid » Fri Jun 29, 2018 3:25 pm

Excellent info Gerry, many thanks...

Hominid
Newbie
Posts: 0
Joined: Thu Jun 28, 2018 6:13 pm

Re: Temperature sensor question

Post by Hominid » Mon Jul 02, 2018 7:06 pm

Hey Gerry (or anybody), wondering if you can point me to the right directory where to put the .pcs file once I've loaded it with the temp/resistance table. I've done the "RTFM" exercise, but can't seem to find it in the documentation.

Thnx...

Gerry
PICO STAFF
PICO STAFF
Posts: 323
Joined: Mon Aug 11, 2014 11:14 am

Re: Temperature sensor question

Post by Gerry » Thu Jul 05, 2018 5:17 pm

Hi Hominid,

The signal conditioning file is not the way to go here. It's a feature intended to be used for sensors that can't use the existing input setup (with pull-ups) for excitation, and need the input signal to be more than just adjusted (e.g. for signals that need amplification so that they are able to be captured).

What you need to do is create a .scl file (scaling file) for use with the 'Parameter Scaling' feature of PicoLog. To do this use the format described (as mentioned) on page 121 of the User Guide (I've included an example below for a 33K thermistor). Then in the 'Edit USB DrDaq Measurement' dialogue box select 'Options', and then 'Scaling', and in the drop down list for 'Scaling method' select 'Use scaling from file', and then select 'File' to navigate to where you have stored your file.

Here is the example:

Scaling file contents (33k thermistor.scl):-

Notes=33kthermistor/100kload/2.5V
Type=Table
Units=°C
Width=3
Places=1
MinValue=-30
MaxValue=30
1.954 -30
1.861 -25
1.753 -20
1.631 -15
1.499 -10
1.359 -5
1.217 0
1.077 5
0.944 10
0.819 15
0.706 20
0.605 25
0.517 30

In the columns of data the first column is the voltage appearing at the input (which in your case will be the value of resistance from your temp/resistance table as the bottom half of a potential divider with 100KΩ in the top half and 2.5V across the divider, or 2.5 * [Rtherm/100k + Rtherm]). The second column is the temperature from the temp/resistance table.

Regards,

Gerry
Gerry
Technical Specialist

Post Reply