-------------------------Monitor------------------------ The Newsletter for PC-Based Data Acquisition and Control Issue 71 www.windmill.co.uk June 2004 --------------------ISSN 1472-0221---------------------- Welcome to Monitor. This midsummer (or midwinter) edition explains how to control electronic equipment. Our main article focuses on hardware issues, whilst the Windmill Notes section discusses which Windmill programs you can use for digital control. We hope you enjoy receiving Monitor, but should you wish to cancel your subscription you can do so at https://www.windmill.co.uk/newsletter.html CONTENTS ======== * Windmill News: Monitor Exceeds 25000 Subscribers * Controlling Electronic Equipment: Relay Switching * Windmill Notes: Digital Output Control Systems * Excel Corner: Automatically Generating Reports II ________________________________________________________ ________________________________________________________ Windmill News: Monitor Exceeds 25000 Subscribers ________________________________________________________ The number of subscribers to this newsletter has now exceeded 25000. Thank you everyone! We launched Monitor in August 1998 and mailed it to just 42 people. Very soon after we started offering our Windmill data acquisition software suite free to everyone signing up. At that time it cost non- subscribers 345 GB pounds to purchase the software - so not surprisingly a great many people took advantage and tried Windmill for free. In fact, around 70% of subscribers still download the software and we've given away over 17000 copies of Windmill! Dedicated to PC-based data acquisition and control, Monitor is sent by e-mail every month. We hope you agree it is written in an easy-to-understand style and provides - articles on making measurements - application examples of computerised data acquisition - tips on using Excel to analyse data - news of exhibitions and conferences relating to data acquisition - links to more information With overflowing e-mail in-boxes we know we have to keep Monitor relevant or you will simply delete it, or worse still mark it as spam. Our yearly surveys have helped us respond to your issues and keep on track. If you don't like what you see - tell us. (We lose around 2.5% of our subscribers a month, mostly through people abandoning their e-mail accounts.) Thanks again for subscribing. ________________________________________________________ ________________________________________________________ Controlling Electronic Equipment: Relay Switching ________________________________________________________ You can use a PC to switch other equipment on and off, according to conditions. For example, say you were monitoring a temperature and wanted to know when it reached a certain level. With a suitable data acquisition and control interface you could use a digital output to - switch on a warning light, - sound an alarm, - telephone a number with a pre-recorded message, - turn off a heater. Unlike analogue signals which continually vary, digital signals are either on or off. Software controls each digital output by just one bit - setting the digital line high or low. At a hardware level, the actual voltage of the high (or low) line depends on its compatibility. The most popular standard is TTL (transistor-transistor logic). This conforms to the following voltage levels for digital output signals. A logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 microA. A logic 0 is represented by 0 to 0.6 V with a current sink capability of at least 16 mA. You'll note that there is a gap between high and low (ie between 2.4 and 0.6 V). This is so the two states are clearly defined. Another term you will come across is LSTTL. This stands for Low Power Shottkey TTL, which as the name suggests has lower power consumption than TTL but has the same logic levels. Why is it important to know whether digital outputs are TTL or otherwise? Because your digital outputs must be compatible with the device you are trying to control. * Switching Relays ================ Computers work at small voltages. To switch a large voltage you would often use relays. A relay opens or closes contacts when a current is passed through a coil, thus connecting or isolating 2 sections of a circuit. A reed relay, for example, consists of two thin magnetic strips (reeds). When a coil close to the reeds is energised, they are magnetised and drawn together making a connection between leads attached to the reeds. Relays are commonly used as signal switches or control switches. Their virtues in these applications being low "on" resistance and isolation between switch and control circuits. For switching heavy loads, many data acquisition and control (DAQ) interfaces have relays on- board. In this case the hardware manufacturer will list in the specifications a "contact rating". This shows the power that can be safely switched with the relay. For example 10 amps at 30 volts DC or 230 volts AC. This must be at least as big as the maximum rating of the device you want to control. The contact rating is quoted for non-reactive load - that is without capacitance or inductance. If you do have an inductive load connected, such as a motor or solenoid, be aware that the contact rating is reduced. This is due to the large transients produced when inductances are switched. You can often reduce the size of the transient by fitting a capacitor in series with a resistor. A situation that often causes trouble is when you switch capacitive loads. A high current rushes into the capacitance when it is switched, often sufficient to weld the relay contacts. If a relay stops working but recovers after being given a sharp tap, then the contact has been welded. People often don't realise when they have a capacitive load. For instance an open circuit screened cable can present a considerable capacitance. If you suspect you will have this problem the you may be able to fit series resistors to limit the peak current. Relays take a significant time (measured in milliseconds) to open and close. Hardware manufacturers quote this as operating time and release time. * Glossary of Terms ================= Signal General term referring to a conveyor of information. TTL Abbreviation for transistor-transistor logic. Provides conditional switching capability depending on voltage levels. TTL-Compatible For digital output signals, a logic 1 is represented by 2.4 to 5.5 V with a current source capability of at least 400 microA; and a logic 0 by 0 to 0.6 V with a current sink capability of at least 16 mA. Output Information leaving a device. Relay Electromechanical device that opens or closes contacts when a current is passed through a coil. Reed Relay Consists of two thin magnetic strips (reeds). When a coil close to the reeds is energised, they are magnetised and drawn together making a connection between leads attached to the reeds. Release Time The time a relay takes to open. Operating Time The time a relay takes to close. Pole A relay contact. Transient A short surge of voltage or current, often occurring before steady-state conditions have become established. Capacitance The ability to store an electrical charge, or, more precisely, the ratio of the total charge on a capacitor to its potential. The unit is the Farad. Inductance The magnitude of a magnetic field created by a circuit element carrying a current. More Information ================ For more information contact Windmill Software Ltd at sales@biodataltd.com. We sell a range of data acquisition and control units providing digital outputs, including the Microlink 751 and 752. These connect to the computer over USB. For details see our on-line catalogue at https://www.windmillsoft.com/daqshop/daq-usb.html https://www.windmillsoft.com/daqshop/resistance.html Other companies, such as Biodata, (http://www.microlink.co.uk/), sell larger systems that can communicate with the PC over greater distances. You can use Windmill software with most Biodata products. ________________________________________________________ ________________________________________________________ Windmill Notes: Using Windmill to Control Digital Outputs ________________________________________________________ Windmill has several programs which you can use to control your digital outputs, including DigitalOut, AnalogOut, Graphics and Test-Seq. Additionally, the Windmill IML Tools make it easy for you control outputs from your own macros and programs. Windmill DigitalOut for Push Button Control =========================================== This software lets you control any number of digital output channels. It provides push buttons for you to change the state of each channel. You can switch each channel individually, or switch several channels at once. For more details see either https://www.windmill.co.uk/digout.html or the DigitalOut Help file available from https://www.windmill.co.uk/help.html Windmill AnalogOut for Controlling Groups of Outputs ==================================================== You normally use AnalogOut to control analogue, not digital, outputs. However there is one special case when you could use it to control digital channels. This is when you have grouped digital channels using Windmill SetupIML. Each digital channel (or line) is initially set to on or off by a single bit. You might, however, want to always switch several channels at the same time - for example to open or close 8 relays at the same instant. In this case you can group the 8 channels together. All 8 relays will be controlled by a single value rather than by 8 separate ON/OFF values. In binary the value would be from 00000000 to 11111111. Bit 0 corresponds to line 0, bit 1 to line 1, bit 2 to line 2 and so on. A value of 1 sets a line to on, a 0 sets it to off. So, for example, to set lines 0, 3, 6 and 7 to on and lines 1, 2, 4 and 5 to off you would send the following number in binary, (best viewed in Courier font so the columns line up correctly): Data bits: 76543210 Binary: 11001001 In hexadecimal you would send "C9" and in decimal "201". For more details see the AnalogOut and SetupIML Help files, available from https://www.windmill.co.uk/help.html Windmill Graphics for Customised Windows ======================================== Graphics lets you design and create your own display and control windows. You can insert buttons to control digital outputs. These can take any appearance you like. There are three types of button: one that toggles between on and off, one that always turns an output on and one that always turns an output off. You can also insert "LEDs" to light up when the output is on. Finally, you can choose whether the the digital output should initially be on or off. For more details see https://www.windmill.co.uk/graphics.html Windmill Test-Seq for Sequence Control of Equipment =================================================== Test-Seq interprets a file of commands and controls equipment and applications accordingly. It can send commands and data to other Windows programs, or directly to the hardware inputs and outputs. The command, or test sequence file is a text file which you can easily create in a text editor or word processor. Use Test-Seq to control digital outputs depending on timing or environmental conditions. For more details see https://www.windmillsoft.com/daqshop/test-control.html Windmill IML Tools ================== You can use the IML Tools to switch digital outputs directly from Windows applications like Excel, from JavaScript code running on a web page, from Visual Basic programs or from any developer tool can integrate Active X controls. Windmill takes care of the communication with the hardware leaving you free to concentrate on your application. For more details see https://www.windmill.co.uk/tools.html All the Windmill programs mentioned can be used with equipment connected to the PC over Ethernet, USB, RS232, RS422, RS485 or Modbus. Contact Windmill Software at sales@biodataltd.com for more information, or fill in the form at https://www.windmill.co.uk/contact.html ________________________________________________________ ________________________________________________________ Excel Corner: Automatically Generating Reports II ________________________________________________________ Last month we explained how to automatically generate reports in Excel. (If you missed last month's copy, you can read it at https://www.windmill.co.uk/monitor70.html) This month we discuss ways to improve the report generation. We show how to implement a form from which people can simply make selections, rather than editing the macro to suit their system. A menu item lets you re-display the form should you choose to hide or close it. Downloading the Report Generator ================================== The improved report generator is available at https://www.windmill.co.uk/excel/reportwl2.zip Unzip this into your Windmill folder. You need to load the worksheet (reportWL_m2.xls) from Excel rather than double clicking on the xls file. Using the Report Generator ========================== When you open the xls file, Excel looks for valid Windmill Logger data files. It considers a file to be valid when you have periodic logging enabled in Windmill Logger, with no files being overwritten. Excel then lets you choose which set of data files to analyse. Make your selection from the File Prefixes box in the opening form. You can then choose how to analyse the data: select the summary type from Maximum value, Minimum value, Sum or Mean. Choose a date for the report and whether the report should cover a day's, a week's or a month's data. Now press the "Make Report" button and Excel will generate the report according to your specifications. Customising the Report Generator ================================ Should you wish to edit the Report Generator - for example to add other analysis functions - click the Hide button on the Report Selector Form. (To redisplay the form select the Windmill menu in Excel and choose "Show Report Selector".) Open the Visual Basic Editor and edit the code attached to the ButtonForm. To create a new analysis function you need to: - Declare it as a constant at the beginning of the macro. - Add it to the drop-down list of functions in the opening form, by editing the UserForm_Initialize() subroutine. - Write the new function using one of the other analysis functions as a template, for example "Public Function analyse_SumColumn(sName, iCol, rowCount)" - Edit the ShowDaily, ShowWeekly and ShowMonthly subroutines to include your new function. For more help with editing the Report Generator see last month's Monitor, https://www.windmill.co.uk/monitor70.html or contact techsupport@windmill.co.uk ________________________________________________________ ________________________________________________________ * Copyright Windmill Software Ltd * Reprinting permitted with this notice included * For more articles see https://www.windmill.co.uk We are happy for you to copy and distribute this newsletter, and use extracts from it on your own web site or publication, providing the above notice is included and a link back to our website is in place. An archive of previous issues is at https://www.windmill.co.uk/newsletter.html and an index of articles at https://www.windmill.co.uk/newsletter.html Windmill Software Ltd, PO Box 58, North District Office, Manchester, M8 8QR, UK Telephone: +44 (0)161 834 6688 Facsimile: +44 (0)161 833 2190 E-mail: monitor@windmillsoft.com https://www.windmill.co.uk/ https://www.windmillsoft.com/
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