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Review: Escort 3146A Bench Top Multimeter Test engineering and research and development work often calls for high-accuracy, high-resolution digital measuring instruments. Bench top multimeters typically used in these applications are very expensive – until now, that is. These new meters from Escort “break the mould” by offering remarkable performance at a relatively low price. By PETER SMITH T HE COST OF these new bench top multimeters is so attractive that they seriously challenge the pricing of top-of-the-line hand-held digital multimeters. Unless portability is a “must have” on your feature list, why would you buy another handheld? Check out these specs: 5½ digits (120,000 count) display resolution, 120ppm (.012% + 5 digits) basic DC accuracy and 1µV to 10mV DC sensitivity. Including the protective holster, the 3146A measures about 255 (W) x 105 (H) x 305mm (D) and weighs slightly less than 3kg. Measurements include DC voltage and current, true RMS AC & AC+DC voltage and current, resistance, frequency, diode test and continuity test. Bandwidth for true RMS voltage measurements is 20Hz to 100kHz. Detailed specifications are presented in the accompanying panel. 76  Silicon Chip In addition to the basic measurements, a number of useful arithmetic functions can be applied to many of the readings. For example, when measuring AC or DC volts, a modifier can be applied to display power in dBm with respect to a reference impedance. The impedance is selectable in 21 ranges from 2Ω to 8000Ω. Other functions include “compare”, “relative”, “minimum”, “maximum” and “hold”, many of which can be combined. For example, if “dBm” and “relative” are selected, the result of the dBm calculation becomes a relative base for new measurements. These meters have five input terminals rather than the three (or four) typically provided on lower performance models. The extra two terminals are for the “sense” lead connections in a four-wire (“Kelvin”) resistance measurement scheme. Using four leads results in double the accuracy that can be achieved with just two leads; as high as 0.05% on the 120Ω scale. Of course, conventional two-wire resistance measurements are also supported. The bottom sense terminal is also used as the positive terminal for current measurements on the mA ranges. In addition, this terminal can be used in conjunction with the main positive and negative terminals to perform 3-wire, simultaneous current and voltage measurements. This could be useful for measuring power in a circuit or the gain of a transistor, for example. Dual VFD display While liquid crystal displays are preferred on portable instruments due to their low power consumption and minimal space requirements, bench top instruments generally employ either LED or vacuum fluorescent displays (VFDs). This meter uses a large, blue VFD that is very easy to read, regardless of lighting levels or viewing position. The VFD incorporates dual readouts that enable simultaneous display of two measurements. The primary (larger) display is always active, where-as the secondary (smaller) display can be programmed to display almost any of the available measurements. www.siliconchip.com.au Specifications (3146A) Basic DCV accuracy of 120ppm 120,000 / 40,000 / 4000 count display resolution (selectable) 2/sec (120,000), 5/sec (40,000), or 20/sec (4,000) measurement rate (selectable) DCV Range from 120mV to 1,000V with 1µV max. resolution ACV Range from 120mV to 750V with 1µV max. resolution DCA and ACA range from 12mA, 120mA, 1.2A to 12A with 100nA max. resolution True RMS AC and AC+DC measurement, ACV 20Hz-100kHz & ACA 20Hz-10kHz Resistance measurement range from 120Ω to 300MΩ with 1mΩ max. resolution 2-wire or 4-wire resistance measurement Frequency measurement range from 1200Hz to 1MHz with 0.01Hz max. resolution dBm measurement with 0.01dBm resolution and reference impedance from 2Ω to 8000Ω Diode and audible continuity test functions Auto or manual ranging Escort 3136A – even better value! So the 3146A looks great, but it’s still outside your budget? Then check out the lower cost 3136A model! It has a display resolution of 4½ digits (50,000 count), a basic DC accuracy of 200ppm (.02% + 4 digits) and a DC sensitivity of 10µV to 100mV. It includes true RMS AC & AC+DC measurements, with an ACV bandwidth of 30Hz-100kHz and an ACA bandwidth of 30Hz-20kHz. Although it has lower resolution and accuracy, the 3136A boasts many of the same features as its bigger brother, including a dual VFD, dbM measurement capability and RS232 interface as standard. For more technical information on the 3136A, check out Escort’s web site at www.escorttw.com Relative mode for zeroing offset Dynamic min./max. recording Compare (High/Low/Pass) function for quick in-tolerance tests Data hold function to freeze readings Standard RS-232 interface Optional GPIB interface 19-inch rack mountable with rack mount kit Fast electronic and closed-case calibration Meets IEC-1010-1 600V CAT II and 1000V CAT I and CE mark The display can be programmed to update 2, 5 or 20 times per second. Display update speed correlates directly with resolution. At five updates per second, the resolution is reduced to 40,000 count, whereas at 20 updates per second, it’s just 4000. High-speed sampling is probably most useful in automated testing, made possible via the communications interfaces (see “RS232 interface” below). On a more basic level, high-speed sampling also makes for virtually instantaneous continuity testing, something that is missing on most of the not-so-cheap microprocessor-based hand-held multimeters! Front panel controls An array of 16 “soft feel” push-button switches is provided for the user www.siliconchip.com.au interface. Most of these perform two roles, the second of which is enabled by pressing a “shift” key first. Unlike some instruments we’ve seen, these meters are relatively easy to drive. Function selections are quite intuitive, with basic measurements possible without so much as a glance at the operation manual. Nevertheless, we do admit to reading the manual before using some of the more advanced arithmetic functions! RS232 interface An RS232-compatible serial interface is included as standard. Essentially, any reading that can be performed at the front panel can also be performed over the serial interface using simple ASCII-encoded sets of commands and responses. At the most basic level, “key” commands can be sent over the interface to simulate front-panel keystrokes. A more involved method uses “set” commands, which control the meter using coded character strings. To retrieve meter readings and instrument status, the “query” group of commands is used. In order to make use of the serial interface, you can either purchase the optional PC link software (not reviewed) or write your own custom applications. An example program showing how to set up the meter and display readings on a PC screen is provided in the manual. Examples for both QBasic and Turbo C are included. An optional GPIB interface is also available for automated test environments. Remote control of the meter over the GPIB bus is described in detail in the operation manual. At time of writing, we’d not had the opportunity to thoroughly test all the features of our 3146A review unit. So far, though, it’s done everything that we’ve asked without a hitch. It’s easy to use, the big blue display is a real treat, and it sure beats our top-of-theline hand-held meter in the accuracy stakes. And it costs about the same! Where to get yours Escort instruments are available in Australia from NewTek Sales, on the web at www.newteksales.com or phone (02) 9888 0100. At time of writing, the Escort 3146A was priced at $990 plus GST, whereas the lower spec 3136A was $600 plus GST. Both models come with a 1-year warranty. Note that these meters are specified with a 1-year calibration cycle. NewTek can help here too, offering local repair and calibration services out of their North Ryde facility. SC March 2004  77