Monitor - ISSN 1472-0221
The Newsletter for PC-Based Data Acquisition and Control
Issue 231, November 2017
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You can download this issue of Monitor as a pdf file from https://www.windmill.co.uk/monitor/monitor231.pdf.
Contents
* Which Range and Resolution to Choose?
* Your Data Acquisition Questions Answered
* Spreadsheet Corner
* Data Acquisition News Round-Up
Which Range and Resolution to Choose?
Web Link: https://www.windmill.co.uk/range-resolution.html
Thermocouples, strain gauge bridges, gas concentation probes and most other analogue sensors produce a voltage signal. This is converted to a form the computer can understand by an analogue-to-digital (A-D) coverter.
Range
The input range (or gain range) of an A-D coverter refers to the maximum and minimum voltage that it can accept.
An input range may be bipolar, covering a range from -10 mV to +10 mV for example; or unipolar, perhaps covering a range of 0 to 10 mV. Most A-D converters have an actual range of 0 to 10 V, so an input signal with a range of 0 to 10 mV needs to be amplified by a gain of 1000 before it can be converted. Many systems offer a choice of ranges, and you can select the most appropriate using software like Windmill.
You should always choose the smallest range that encompasses your signal, as this optimises the resolution.
Resolution
The resolution is the number of steps into which the input range is divided. The resolution is usually expressed as bits (n) and the number of steps is 2n-1. This equates to (2n) values. A converter with 12-bit resolution, for instance, divides the range into 212, or 4096, values. In this case a 0-10 V range will be resolved to 2.5 mV, and a 0-100 mV range will be resolved to 0.025 mV.
Although the resolution increases when you narrow the range, there is no point in trying to resolve signals below the noise level of the system: all you will get are unstable readings.
Some A-D converters have a choice of resolutions (offering 12-, 13-, 14-, 15- and 16-bit for example). You can choose the most suitable for your application, balancing speed against accuracy.
For more data acquisition tips and techniques, see the Windmill web site at https://www.windmill.co.uk/
Your Data Acquisition Questions Answered
Question
"We have several connectors all using a rs232 connector to get data from the devices we support. At the moment all devices use manufacturer specific software to retrieve this data and all are outdated and do not work on Windows 10.
Does your software work on Windows 10 64-bits?
We need to connect those RS232 devices to a USB port of the new PC. Which hardware would you recommend to make that connection?"
Answer
Yes, Windmill software works on Windows 10 64-bits. You can use most types of RS232-USB converters, as long as they have an option to continually provide data rather than buffering it.
More on the software and the instruments it works with is at https://www.windmillsoft.com/daqshop/rs232-modbus.html
Spreadsheet Corner: Customising how data is displayed depending on values
These tips apply to both Excel and Calc (OpenOffice and LibreOffice).
You can set a cell format to, for example, apply different colours to different temperature values. Select your range of cells then from the Format menu select Cells
In Excel: Choose Custom and enter into the Type box
[blue][<0]-0.# "oC";[red][>30]0.# "oC";[black]0.# "oC"
In Calc: Enter into the Format code box
[blue][<0]0.# "oC";[red][>30]0.# "oC";[black]0.# "oC"
This will colour temperatures less than 0 oC blue, temperatures above 30 oC red and other temperatures black.
The colours you can choose from are: cyan, green, black, blue, magenta, red, white or yellow.
The "oC" specifies that oC is added after every data value.
The 0.# will show the data to 1 decimal place, with a leading zero if necessary.
You could achieve something similar with the Conditional Formatting box, but this way gives you more options.
For more spreadsheet tips see https://www.windmill.co.uk/excel/ and https://www.windmill.co.uk/openoffice.html
If you have an Excel question contact monitor@windmillsoft.com.
DAQ News Round-up
Welcome to our round-up of the data acquisition and control news. If you would like to receive more timely DAQ news updates then follow us on Twitter - @DataAcquisition - or grab our rss feed.
Marine sensors funding to help probe mysteries of the deep
Sensors that are compatible with autonomous underwater systems such as NOC's autosub Boaty McBoatface will be able to perform a variety of functions at sea, helping answer questions about our changing oceans.
Source: SCUBA News
http://news.scubatravel.co.uk/
Sensors applied to plant leaves warn of water shortage
Electronic circuits reveal when a plant begins to experience drought conditions.
MIT
http://news.mit.edu/
A Speed Gun for Photosynthesis
How fast is that plant pulling carbon dioxide out of the atmosphere? You may soon be able to point a sensor at it to find out.
Source: NIST
https://www.nist.gov/
Printable bacteria used for low-energy biosensors
UK researchers have used bacteria as a solar-harvesting ink to print paper-based disposable biosensors.
Source: Duke University
https://pratt.duke.edu/
Virtual cocktails hijack your senses to turn water into wine
Using a combination of LEDs, electrodes and smelly gas, the Vocktail can simulate a variety of flavours to create digital drinks
Source: New Scientist
https://www.newscientist.com/
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