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Automotive Product Review The Brymen 328 automotive multimeter Electronic engine management systems require special tools for fault diagnosis. Here we take a look at the Brymen BM328 Automotive Meter. It includes a range of useful diagnostic functions, including the ability to measure fuel injector pulse width. By JULIAN EDGAR When woring on an electronically managed car, a multimeter is vital for diagnostics and fault finding. Even the simplest multimeter will be of some use but a more sophisticated unit will add functions which can prove very helpful. Specifically, an automotive multimeter should – in addition to "normal" multimeter functions - have the ability to read pulse width, duty cycle, frequency, engine rpm and temperature. Less exotic – but still useful – is a DC current range which extends up to at least 20A. Meters with these functions have been available for some years but their cost (generally $500 or more) has precluded their use by home-based mechanics. That situ­ ation has now changed following the release of two new automotive multimeters -the Brymen BM323 and Brymen BM328 -at a much lower cost. The Brymen BM323 is the cheapest of the two and includes the following facilities: • DC Volts (200mV-200V); • Resistance (200Q-2MQ); • DC Amps (0-20A, 30 seconds on, 5 minutes off measuring cycle); • Duty cycle (0-100%); • RPM (requires optional inductive pick-up); • Dwell Angle (4, 5, 6 & 8 cylinders). The Brymen BM328, which is the subject of this review, adds the following features to the above list: 16  Silicon Chip Above: testing showed that injector pulse width could only be measured when the fuel injector was actually connected into circuit. Probing the disconnected loom plug gave false readings on this meter, although interestingly this does not occur on a (much more expensive) Vane unit. • • • • • AC Volts (200mV-500V); Temperature (requires optional K-type thermocouple); Pulse Width to 200ms; Dwell Angle (3, 4, 5, 6 & 8 cylinders); Frequency (2kHz-100kHz). Main features The Brymen BM328 Automotive Meter comes in a protective, bright-yellow rubber holster. A set of leads is supplied and these are equipped with screw-on alligator clips in addition to the normal pointed probes. This is useful in that much automotive measuring requires a hands-free fixed attachment to the wiring. A 51-page (but they are very small pages!) instruction manual is also included. At first glance, the BM328 looks like a conventional multimeter. It has a 3.5-digit (1999 count) liquid crystal display (LCD), a large rotary selector switch and the The optional inductive sensor costs $32.95. It clips over a sparkplug lead & allows the engine speed (ie, rpm) to be measured. The Brymen BM328 automotive multimeter is supplied in a soft rubber holster & with leads. At $239, the unit is considerably cheaper than other autoomotive multimeters with comparable functions. usual array of input sockets. Immediately below the LCD are eight pushbuttons and these provide the following func­tions: (1) RPM selection (either 2-stroke or 4-stroke, with 4-stroke default); (2) internal fuse test; (3) maximum read­ing hold; (4) hold for the current display; (5) toggle be­tween triggering on the negative or positive slope when in pulse width or duty cycle modes; (6) trigger level (allows frequency-based functions to be triggered at either 3.1 V or 10.5V; (7) auto power-off disable; and (8) selection of secondary functions shown on the rotary knob display. The maximum hold feature is useful when only the peak value is of interest, with the meter able to be used as a simple data-logger in this mode. An example of where this would be useful in an automotive application is when using the optional K-type thermocouple. Measur­ing the peak inlet air temperature to the engine could be done by locating the meter securely under the bonnet, with the thermocouple located in the intake air duct, and then actually driving the car on the road. Incidentally, the higher this temperature the less dense the combustion air will be – leading to a reduction in potential peak power. The ability to disable the automatic power-off function is useful where engine monitoring is being undertaken for periods longer than 15 minutes. For example, it would normally take at least this long to measure a coolant temperature sensor's output over its full range by starting and then idling the engine. There's nothing more annoying Fig.1: an example of the sort of data that can be measured with the Brymen automotive multimeter. This graph shows the injector duty cycle of a Subaru Liberty RS in a variety of driving conditions. Generally, the injectors are open for less than 10% of the time but at full throttle in the modified car, the duty cycle exceeds 90%. July 1995  17 The probes are supplied with insulated screw-on alligator clips to allow hands-free circuit connections. The instruction book uses a tutorial approach to show how the unit is used to take various measurements. than a meter which constantly switches itself off at the wrong time, particularly when conducting on-road tests. The main rotary selector knob has no less than 30 positions (including OFF). As a result, the markings around the knob are quite small. What's more, the pointer mark­ing does not wrap around the edge of the knob, which means that care must be exercised to ensure that the desired range is indeed selected. A small dab of white paint on the side of the knob would alleviate this prob­lem. Below the range selection knob are the four input jacks. These comprise (from right to left): (1) common, (2) posi­tive input for all functions except current; (3) ground reference for the thermocouple; and (4) current input. Note that banana jacks are used here for the thermocouple instead of the more usual dedicated thermocouple socket. A minor irritation is the unwarranted use of irrelevant inscriptions close to the input sockets. The distractions include legends indicating that the meter has an auto power off function, that it is water resistant, and that it beeps if the jacks are incorrectly placed. All of these are useful features but there's no need to have inscriptions to this effect cluttering the front of the meter! The meter's main selection knob has no less than 30 positions. This, together with the fact that the knob's white line does not wrap around its edge, makes quick selection of specific ranges a little haphazard 18  Silicon Chip Using the meter The instruction manual briefly covers each of the meter's functions and then shows how the meter is used by a series of tutorials. The first, for example, shows how the meter is used to measure the battery voltage and, based on this measurement, describes the conclusions that can be drawn regarding the state of the battery. Other tutorials show how to measure engine rpm, dwell, the voltage across the points (for those with old cars), and so on. The manual is generally clear and well illustrated. One aspect which caused some initial confusion was the measurement of duty cycle and pulse width. These measurements are required when checking fuel injector pulses, for example. There are two important points to note here: (1) the meter is polarity-conscious when meas­uring these parameters; and (2) it will not give a valid reading unless the injector is in the circuit. As an example of the latter point, if an injector plug is removed from the injector and the meter connected to this plug, invalid results will be obtained. This is not the case with some other automotive multimeters. This "problem" is easily overcome by reconnecting the fuel injector, after which the correct reading will be obtained. This also appeared to be the case with the frequency measurement – at least on one test car. To be fair though, the handbook does show the injector connected (and polarity markings are visible) in the diagram for pulse width measurement. The remaining functions of the meter, including the use of the optional inductive pickup for measuring engine rpm, all worked without any initial problems. Considering its relative cheapness, the Brymen BM328 Automotive Meter is a good buy for anyone interested in general tune-up work and fault diagnosis in engine management systems. The unit (Cat. QM-1450) costs $239, while the Brymen BM323 (Cat. QM-1440) costs $159. The optional inductive pick-up (for rpm measurements) costs $32.95 (Cat. QM-1455), while a suitable thermocouple probe is available for just $12.95 (Cat. QM-1282). For further information on the Brymen meters and acSC cessories, contact your nearest Jaycar store. SILICON CHIP BOOK SHOP Newnes Guide to Satellite TV 336 pages, in paperback at $49.95. Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Servicing Personal Computers By Michael Tooley. 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