-------------------------Monitor------------------------
The Newsletter for PC-Based Data Acquisition and Control
Issue 166 www.windmill.co.uk May 2012
--------------------ISSN 1472-0221----------------------
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CONTENTS
========
* Windmill News: Interfacing an
Adam 4018 Thermocouple Input Module
* COM port settings
* Excel Corner: Closing All Open Worksheets
* DAQ News Round-up
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________________________________________________________
Windmill Notes: Interfacing an
Adam 4018 Thermocouple Input Module
________________________________________________________
The latest addition to the list of instruments interfaced
by Windmill, is the Adam 4018 Thermocouple Input Module
from Advantec. You can use an RS485 to RS232 converter
to connect the module to the computer.
To log and chart data from the Adam 4018, download
Windmill and enter these settings.
COM Port Settings:
Baud Rate: 9600
Data Bits: 8
Parity: None
Stop Bits: 1
Flow Control: None
Data Format:
Prompt String: #000<CR>
This command asks for analogue input data from
module address 00, channel 0, where <CR> is a
carriage return.
Example data string:
The module will send back a reply in the format
>+026.60<CR>
To extract just the reading, including the +/- sign, use
Ignore Until +-
Extract Until <CR>
Instrument Timings:
Read: Directly
Timeout: 5000 ms
Instrument Idle or Wait Time: 500 ms
Data Persistence Time: 5000 ms
For more information see
https://www.windmill.co.uk/driver-adam-advantech.html
For how to use Windmill with other serialinstruments see
https://www.windmill.co.uk/serial_driver.html
For more on RS232 connections see below and
https://www.windmill.co.uk/rs232-communication.html
https://www.windmill.co.uk/handshaking.html
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Making Measurements through the COM Port
________________________________________________________
You can connect many different types of industrial and
scientific instruments to computers via their COM ports.
Doing so lets you automatically transfer data directly
into logging, charting, spreadsheet, database and other
display and analysis programs.
To achieve this you need some driver software to read
the data arriving at the port. You can download a free
trial of Windmill software.
When using any serial driver you will need to tell the
software about the communication settings used by your
instrument. These include COM port number, baud rate,
parity, data bits and stop bits.
*
Most Common Settings
The most commonly used settings for serial devices are...
Data Bits: 8
Parity: None
Stop Bit: 1
Flow Control: None
Read on for an explanation of these and other
COM port terms.
*
COM Port Number
You need to tell the software into which port you
have plugged your instrument. If your computer does not
have any COM ports, or you have more devices than you
have ports, you can easily add a USB-serial adaptor
(more details at https://www.windmill.co.uk/usb-serial.html).
*
Baud Rate
In serial communications - such as through the
COM port - messages are sent 1 bit after another.
The baud rate specifies how frequently the bits are
sent. The instrument and the computer must
both communicate at the same rate. The driver software
will always offer a choice of baud rates: pick the
one matching your instrument's. If you can select the
baud rate of your instrument it is best to choose a
fast rate. This reduces the transmission times when s
ending and receiving messages. If the instrument is a
long way from the computer and transmissions are
unreliable, you may need to use a lower baud rate.
No matter how fast your connection - the maximum number
of instrument readings per second depends on the software.
*
Data Bits
The stream of bits received at the COM port is
interpreted in groups of (usually) 7 or 8 bits.
Each group represents a piece of information. It is
obviously important that the instrument and the
computer concur on the number of data bits in a
group. You will have to consult your instrument's
manual to find out how many data bits it uses.
If you are unsure, set the driver software to the
more commonly used 8 data bits.
*
Parity
Parity is the state of being either odd or even.
In serial communications parity may be used to check
for errors in the transmission of data. When performing
a parity check, the instrument or PC sending messages
counts the number of 1's in a group of data bits.
Depending on the result, the value of another bit -
the Parity Bit - is set. The device receiving the data
also counts the 1's and checks whether the Parity Bit
is as it should be.
To perform a parity check the computer and the instrument
must obviously agree on how they are calculating the
Parity Bit. Are they setting it on for an even or
odd number of 1's? When a device uses Even Parity, the
data bits and the parity bit will always contain an even
number of 1's. The reverse is true for Odd Parity. For
example, when Odd Parity is operating and the data bits
contain 10010110 - we have four 1's so the parity bit
will be on (set to 1) to make an odd number.
Two other parity options often available in driver
software are Mark and Space. These aren't effective in
error checking. Mark means the device always sets the
Parity Bit to 1 and Space always to 0.
Parity is a rudimentary error checking mechanism. It
can detect an error in transmitting 1 bit, but if 2 bits
happened to be wrong it would not pick this up. It also
provides no help as to which bit is wrong. Other error
checking mechanisms include the Start and Stop Bits
described below, and cyclic redundancy checks which are
often used in Modbus communications.
Consult your instrument's manual to determine its parity
settings - if in doubt start by setting parity to "none".
No Parity Bit will be sent.
*
Start and Stop Bits
Communication through the COM port is asynchronous. This
means that data is sent intermittently and not at
predetermined intervals. A device must therefore be able
to determine the start and end of a message. It accomplishes
this by Start and Stop Bits. The start bit precedes the
data bits. The stop bit follows either the parity bit if
present, or the data bits.
The data line has two states - on and off. An idle line is
always on. When the instrument or computer wants to send
data it sets the line to off - this is the Start Bit. The
bits immediately after the start bit are therefore the
data bits.
The Stop Bit is present to allow the instrument and computer
to re-synchronise should anything go wrong: noise on the line
masking the start bit for example. The period of time between
the start and stop bit is constant, according to the baud rate
and number of data and parity bits. The stop bit is always on.
If the receiver detects an off value when the stop bit should
be present, it knows there has been an error.
The stop bit is not actually 1 bit but a minimum length of time
the line must be on at the end of each data transmission. On PCs
this is normally equal to 1 or 2 bits, and you must specify
this in the driver software. Although 1 stop bit is most common,
selecting 2 will at worst slow the message down slightly.
(You might see an option to set the stop bit to 1.5. This is
only used when the number of Data Bits is less than 7. If this
is the case then ASCII characters cannot be transmitted and so
1.5 is rarely used.)
*
Flow Control (Handshaking)
Unless you know differently, when connecting the instrument
to the PC it is best to start with the assumption that flow
control is not required.
If you start with no flow control what symptoms might
indicate that it really is needed?. One possibility is
that the instrument misses part of a message sent by the
computer. This will probably cause the instrument not to
work properly.
If flow control is required it will most commonly be
Xon \ Xoff (software).
________________________________________________________
________________________________________________________
Excel Corner: Closing All Open Worksheets
________________________________________________________
To close all worksheets at once, but leave Excel open:
1. Hold down the shift key on the keyboard and select
Excel's File menu.
2. Choose the Close All option which has appeared.
For more Excel tips and tricks, see
https://www.windmill.co.uk/excel/
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________________________________________________________
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 either grab our RSS
newsfeed at
https://www.windmillsoft.com/monitor.xml
or
follow us on Twitter at
http://twitter.com/#!/DataAcquisition
Robotic fish shoal sniffs out pollution in harbours
Autonomous robotic fish designed to sense marine
pollution, have taken to the open waves for the first
time. Working in a group, the fish can cover a
1 km-square region of water, down to a depth of
30 metres. They communicate with each other and a
nearby base-station using very low-frequency sound
waves, which can penetrate the water more easily
than radio waves.
Source: New Scientist
http://www.newscientist.com/
Meter enables cost-effective monitoring of energy usage
A new device could help manufacturers monitor their
energy usage more cost-effectively using technology
originally created for washing machines. The new
meter uses a 3D sensor, originally developed to
monitor the position of washing-machine drums, that
measures the magnetic field created by an electric
current in the parallel direction as well as the
perpendicular, making it more accurate than
previous designs.
Source: The Engineer
https://www.theengineer.co.uk/
90 Million Homes Worldwide Will Employ Home Automation Systems by 2017
New subscription-based home automation offerings
are rapidly transforming the way consumers will
monitor, secure, and control their homes.
Source: ABI Research
http://www.abiresearch.com/
Food, Water Safety Provide New Challenges for Today's Sensors
Sensors that work flawlessly in laboratory settings
may stumble when it comes to performing in real-world
conditions, according to researchers. While sensors
are becoming increasingly sophisticated, little or no
field testing has been reported.
Source: Newswise
http://www.newswise.com/
New Point for Dew Point
The Physical Measurement Laboratory has devised a
new humidity generator that enables dew-point
measurements up to 98 °C – a substantial extension
above the previous limit of 85 °C – and provides
expanded calibration services for hygrometers in a
variety of industries.
Source: NIST
https://www.nist.gov/pml/div685/dewpoint.cfm
________________________________________________________
________________________________________________________
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