Data loggers. Modern recorders

Data loggers recorders Today's industrial processes generate vast levels of data, in both analogue and digital form, which need constant monitoring and analysis. The data logger has evolved to meet this need, both on its own and as part of a dataacquisition system by Glenis Moore limited in what they could connect to each channel. During the late 1960s the first selfcontained'logger was introduced. It incorporated a printer, scanner and digital multimeter (DMM), and was programmed via the front panel. Since that first appearance, the data logger has continued to advance, giving increased programming ability, multiple linearisations for thermocouples, multiple input ranges etc. The function of a data logger is to access the output from a number of transducers and convert the measurement into a form that can be recorded. All the inputs must produce a DC signal, but apart from that many different transducers, -e.g. straing gauges, thermocouples etc., can be accommodated. Most modern loggers consist of the following basic circuit elements (see Fig.l): • signal conditioning, which consists of the circuits used to scale a&d 'clean up' the input signals and, occasionally, power supplies for bridge networks • multiplexer, which acts as a switching arrangement to sample each channel in turn • measurement circuits, which monitor the magnitudes of the input signals and output signals to identify the channel on a display and the magnitude and sign of the measured parameter • convertor, to convert the analogue input signals into a digital signal • timing and control, to control the rate of sampling and switch the system through the channels. The microprocessor has enabled an enormous increase in the programmability of data loggers. This in itself has created a problem of how to gain access to these program options. Confusion Current data loggers fall into three categories: button-per-function loggers, menu-driven loggers and the loggers programmed using a computer language such as Basic. Th$ oldest of tfeese $ the button-per-function logger, in which the unit's facilities are predefined. But as loggers and their capabilities become more complex the$e instruments present the user with an ever increasing array of buttons, which can lead to confusion. Menu-driven- loggers were conceived to alleviate the problem of this array of buttons by presenting the user with a smaU screen and either hard or soft keys to select different levels of functions. ©IEE: 1986 However, this type of instrument still suffers from the restriction of having all its functions predefined; If a logger is programmed using a computer language it can be enabled for practically any function, The problem exists, however, that the user has to have a knowledge of programming, and writing programs takes time. Some loggers combine menu-driven screens . with computer-language programming to increase the instrument's capabilities while making it easy to use by people with no computer programming skills. Small data loggers (with less than 20 channels) seem to rely almost entirely on the front-panel button-per-function approach (see Table 1), although many incorporate facilities for remote programming via an IEEE 488 or RS232C interface. As the number of channels increases, menus, or function buttons plus prompts, become more popular (see Table 2) with computer-language loggers having usually more than 100 channels (see Table 3). Digital As far as inputs are concerned almost all modern data loggers can linearise most thermocouple types and handle thermistor inputs. Additional facilities on some models include complex sellings for such parameters asflowand differential pressure, Many manufacturars also incorporate digital input chamitls in their instruments for monitoring such things as contact closures. Although previously known as a chartrecorder manufacturer, Gulton Ltd. h&m recently ventured into data loggers wtlfa the launch of its handheld Quart©! logger. The unit features four input channels, all of which accept analogue data and three of which accept digital information, two front-panel switch*! to' select and enter data, and an adaptiw memory system whereby it only reoordto Table 1 Small data loggers (up to 20 channels) company product channels programming interfaces remarks price Gulton Quartel up to 4 front-panel buttonper-function RS232C data analysed via IBM of iBMcompatible PC . £399 (with d t t i analysis softw&rt) Grant Squirrel 2-16 (depending on model) front-panel buttonper-function 8-bit parallel or RS232C data analysed via external computer £400-800 Royston Electronic Systems 800 Information Retrieval System keypad button-perfunction RS232C can accept inputs from most sensors £1200 1600 Series Autoscan minimum 16 front-panel buttonper-f unction RS232C(2) can foe extended to incorporate high and low alarms on each channel £1825 Datacapture Datablock (DB4000) 16 button-per-function with user prompts RS232C IEEE488 (options) measurement resolution equals i/4000th of input range for analogue or 24 bits for digital £2990 Wykeham Farrance Engineering Ltd. System 91 Autotech from 8 front-panel buttonper-function RS232C(2> designed specifically with civil engineering applications in mind approx. £3106 Thorn EMI MLX Instruments (AD Data Systems Inc.) up to 10 front-panel controlper-function RS232 features a weathertight case. Uses include solar energy, pollution monitoring and powertransmission studies £2396 Bristol Industrial Digilog 104 & Resarch Associates Ltd. (Digi-logger GmbH) 1 -8 input modules front-panel buttons guided by displayed prompts RS232C IEEE488 IEC625 incorporates integral printer for plotting data in graph format £4000-7000 A.B.I. Data Ramlog Ep8000 8 or 16 with add-on multiplexer via external computer parallel and includes 16 kbyte adaptor for memory and RS232 3H-dig1t LCD approx. £600 Solartron Instruments Imp modules 10 or 20 via external computer adaptor card to IBM PC used with IBM PC (or similar) to form distributed logging system £895-1050 Interface card £685 Skye Instruments Ltd. SDL 600 program stored on EPROM, altered by on-board dual-inline switches RS232 parallel designed for use by biologists and ecologists, waterproof, battery operated approx. £1000 Delta Technical Services Ltd. Celia via external PC using Delta's own modem RS232 designed originally to measure flow rates in the water supplies industry; water resistant to 1 m (IPC67); 10 year battery life £334 interface and software £839 Data & Research Services pic PDL10 up to 4 keypad plus display prompts RS232 8 bit parallel stored data can be collected via removable memory module or telephone £2000-2500 Fluke 1752A up to 16 Fluke Basic via keyboard supplied RS232C IEEE488 basically a DAS with touchscreen operation at speeds up to 400 readings £8731 Centronic r' I •>?. 1 »I.J»V, jand Ift^f * • ' i ; ' . ! t'cH-X t , - - : '" ^ " Mi$ y ,..••• v M \ ^ Is* * - t ; - ^ . - ' - • ^ •. • • ' • * - • " • • ' • - f e ••-• • ' • • • ' - i • • ••' ' • " - ' • ; ( M • • - •-<••.-• . ^ ^ . ..*...«^.,~ ^ gi« - 'v,.1 , j «? « >®M-I£*i , r • - , : •. • • . < , ' . .j> • * % .TI. ...VAV- or -a« V.v •^''..^ ?^ . '* »" > 4 \ 'titV . Vt.-'j «p sists of a microcomputer and analogue/ digital input/output modules, and can be programmed using Basic, Pascal or C, A standard data-logging application program is also available for the system, which enables channels to be set up using simple menus. The Magna 2000 from Leeds & Northrup International is billed by the company as an intrinsically safe process plant scanning, alarm and logging system which is designed for such industries as power, petrochemical and steel processing. It incorporates a DEC PDP11 microcomputer and can scan up to 1000 inputs to provide data displayed either on screen or in a formatted printout. The Logpac 2001 from Datron Instruments consists of a system controller, with integral disc drive, external keyboard, graphics plotter and printer, and a system scanner which incorporates input modules for up to 200 channels. It is programmed, via the keyboard, using menus with screen prompts and error reporting, and supports thermocouple, resistance-thermometer and straingauge measurements alongside a userprogrammable input that can be enabled for a transducer peculiar to the user's application. Retailing at £77S0 plus VAT the system also enables highor low-alarm limits to be allocated to any channel. Data-acquisition systems are also used for monitoring and recording telecommunications networks. Shrewsbury Electronic Engineers Ltd* is particularly active in this area, with around 50 such systems operating within the British Telecom network. Many processing companies use large loggers and data-acquisition systems, connected via a network, to monitor their plants. This does away with &e need for someone to walk round the site taking measurements and also offers much greater accuracy as a logger is always (on duty'. If a fault occurs, the central system can be notified Immediately and corrective action taken. BP oh Arctic field trials distributed system, whereas the 2285B is a more economical version for applications where fewer than 100 channels are required. Both models are programmed via prompted menus and have optional IEEE 488 and RS232C interfaces to enable remote programming; the 2280B also incorporates a cartridge tape-drive system for data and program storage. The data-acquisition system (DAS) has been more prolific since the emergence of the personal computer as such a system invariably uses a PC or a computing facility of some sort for dataanalysis/programming. The average DAS offers more flexibility than a stand'Data loggers that can handle more alone logger but it is usually more dif) channels $eem to vary consid- ficult to program. fn programming methods, Many established data-logger manuthe trend seems to be drifting facturers are now offering data-acquisia limited amount of tion systems alongside their loggers, inprogramming. This cluding Fluke whose 1752A DAS is I'" 3* pma&hly highlighted by the increasing slightly unusual in that it incorporates vt $$@3p«tit!an to instruments from more most of the computer facilities inside the developed data-acquisition logging device, with only the keyboard i, which incorporate both an in- as a separate unit. Programming is logging device and a personal achieved using Fluke's own version of Black box lor programming. Basic, with touch-screen operation for The data logger and data-acquisition TKt basic Orion A logger from Solar- such functions as running programs. 16 system are now almost oommonplac© in tjteosi instruments! can handle up to 200 in- differential analogue measurement laboratories, field-service tool kits, profyad Is programmed locally using channels can be scanned by the 1752A cessing plants etc., in fact anywhere that buttons and display prompts. It at a speed of 100 readings per second, requires the recording of large quan^teoorporates' a strip printer and with speeds of up to 400 readings per se- tities of data. Practically any type of f .jBB«$aaetSc-t®pe cartridge a$ standard and cond achievable when extra analogue analogue (or digital) signal can be be controlled remotely via an IEEE measurement processor boards are in- sampled, and even small loggers offer or RS232C interface. Solartron also cluded. Retailing at £8731, the 1752A some sort of data analysis and/or manipthe Orion Delta logger falls into the same price bracket as a 200 ulation. Gone are the days of endless U vvtf similar to the Orion A ex- channel data logger, but what it lacks in handwritten pages of results, hours of that it incorporates an extensive channel capacity it makes up for in data- drawing graphs or performing simple ^-processing facility and uses Basic- manipulating ability. calculations on each result,* the®© timeentered via the front Woking-based PPM Instrumentation consuming functions have been sucI, to manipulate the data. Both log- Ltd. supplies a multiuser /multitasking cessfully replaced, at least in most inoan accept inputs from thermo- logging system called Magus, which can stances, by yet another electronic 'black i, resistance thermometers, strain scan up to 1000 analogue inputs. It con- box'. \ $&uge« %nd many other devices. In the spring of 1985, Fluke introduc- Bibliography •..*$& new family of data loggers known as x V'0® 2280 tefle®. There are two models in SKINGLEY, D.: Data loggers', C&I, May 1985, pp.31-33 ? '•'-"• ' s;the2280Bandthe2285B. The FABER, M.: 'Trends in data acquisition', Test &Meas. World, Oct. 1984, pp.57-64 can be 9xp&nd&d to a 1500-point WOOLVET, G.A.: Transducers in digital systems' (Peter Peregrinus Ltd., 1979) $#l&ittrY of Agriculture, Fisheries & ordered one of these instruments the Idea ol using it to monitor the g its-of birds. As cine film and :"IJaah guns upset the birds, it is planned t& install the logger, complete with infram& aertsors, just outside the entrance to $ sealing box. The experiment is part of t 5-y#ar investigation into the effects of /©•real insecticides on small birds, •specially the feeding habits and .!se**ditig success of tree sparrows which cm insects in areas where crops Above average 171 Average 172 Below average |78