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Tektronix DMM4050 6½ Digit Precision Multimeter This bench-top multimeter features 6½ digit readings, a graphic LCD and a number of advanced features such as trend plot, histogram and dual measurement mode. With front and rear panel inputs, its short term and 1-year accuracy figures are outstanding. Review by Nicholas Vinen siliconchip.com.au May 2010  79 T he Tektronix DMM4050 has all the usual features you would expect in a high accuracy bench-top multimeter. The main modes are DC voltage and current, AC voltage and current (with true RMS), resistance (2- and 4-wire), continuity, diode testing, capacitance and temperature. Temperature measurement is via RTD (resistance temperature detector) only and can be use 2-wire or 4-wire sensing. The unit measures 225mm wide, 330mm deep and sits 150mm above the bench surface when using the integrated carrying handle as a tilting bail (which provides two different angles). It comes with a pair of high quality needle probes, a power cable, an RS-232-to-USB cable and two CDs with documentation and software. A calibration certificate is provided along with a booklet that contains installation and safety instructions, as well as listing the accuracy figures. The basic DC voltage precision is 0.0024% over one year; other modes feature similarly excellent figures. Maximum DC voltage resolution is down to 100nV and DC current to 100pA. Also on the rear panel are the external trigger terminal block, the Ethernet, RS-232 serial and GPIB (General Purpose Interface Bus) ports, the IEC power connector and the power switch. All functions (including power on/off) are easy to access via the front panel buttons. The interface response is instant – the only time there is a noticeable delay is the first time the unit is turned on after being connected to mains power. In any mode, extended functions are generally provided via the five “soft buttons” which are labelled at the bottom of the LCD. This allows them to change function to suit the mode. Less commonly accessed functions are available via the “Analyze”, “Measurement Setup” and “Instrument Setup” buttons. Features One of the more outstanding features of this unit is the display. It is a wide-format cyan-on-black graphic LCD which is easily visible from any angle. There are three brightness settings available. Having a graphic (dot matrix) display means that the format can change depending on the mode. For example, a larger font is used when taking a single measurement compared to dual measurement mode, making the display easier to read. The display also permits graphical features such as the trend plot and histogram. In addition to the six banana sockets on the front, there are five on the back; the low current sense terminal is duplicated but the 10A terminal is not. Two buttons on the front panel switch between the two sets. This could be used for several purposes, eg, to switch between different sets of probes or for connection to an external test interface with less clutter. Virtually all modes provide optional digital and analog filters to remove noise and high frequency variations from the readings. AC measurements can also be displayed in dB or dBm and have more filtering options. The diode tester has a few selectable voltage and current levels. Most modes give a choice of 4, 5 or 6-digit readout and you can configure how many power line cycles (PLC) the readings are sampled over, for a speed/accuracy trade-off. The longer the sampling time, the less noise affects the reading. The DMM4050’s dual measurement mode is handy but more limited compared to some other bench meters. In DC volts mode you can also measure AC volts. In AC volts or amps mode you can measure the DC component or frequency simultaneously. In DC amps mode you can measure AC amps, DC volts or volt-amps. In frequency mode, period can also be displayed. In temperature mode, the sensor resistance can be displayed. In DC volts mode, the default input impedance is 10MΩ but it can be set to 10GΩ for the 10V range and below. This could be critical for getting accurate readings on a voltage with a high source impedance. There is another very useful DC voltage measurement feature: the sense terminals can provide a reference voltage and display the reading as a ratio to it. That could be Fig.1: this PC screen shot of the provided software (“NI LabVIEW SignalExpress Tektronix Edition” Light Edition for Windows”) shows the real-time reading taken from the DMM4050 along with the control panel which allows you to configure it from the PC. A USB-to-RS232 serial cable is also included. Fig.2: the software can log measurements over time and display them in an auto-scaled graph which is updated as measurements are taken. Display, inputs & controls 80  Silicon Chip siliconchip.com.au control the meter and record the readings (see Fig.1 & 2). Serial interface protocol documentation is also provided. This allows custom software to be written which has full control over the meter. For example, such software could allow for automated testing in a production environment. While the built-in trend plot and histogram features of the meter are impressive, off-loading the data to a personal computer for analysis or plotting provides a great deal more power and flexibility. The busy rear panel of the DMM4050. Along with the second set of inputs, there are the external trigger terminal block, the Ethernet, RS-232 serial and GPIB ports, the IEC power connector and the power switch. handy for measuring voltage dividers etc. The capacitance measurement range is from 1pF to 100,000F – allowing measurement of virtually any capacitor you might come across. The meter has quite a few mathematical and analysis features. Mathematical options include limit testing, offset nulling, arbitrary offsetting, ratio measurements and mX+B measurements. An interesting feature is “stats” mode which shows reading minimum, maximum, average and standard deviation over a configurable number of samples. The DMM4050 can be triggered from an external source and can also send a pulse after each measurement is completed, via the 3-way terminal block mounted on the rear panel. The trigger delay and number of samples collected when triggered are adjustable via the front panel interface. Storage and logging The DMM4050 has a 10,000 reading internal memory and can also store multiple configurations internally, to save time repeating particular test set-ups. If a USB flash drive is plugged into the front panel, it is possible to store another 999 files with the same 10,000 reading limit for each. This provides a handy way to get data to a computer for analysis regardless of where the meter is installed. Readings can also be saved to a USB flash drive from the internal memory. The unit can be controlled and measurements taken from a computer via an RS232 serial interface, GPIB or over Ethernet. The supplied RS232-to-USB adaptor cable makes connection easy with virtually any modern computer. “NI LabVIEW SignalExpress Tektronix Edition” (Light Edition) Windows software is included. With it you can Clever accessories The DMM4050 has a very clever optional accessory – the TL705 4-wire test lead. It has just two banana plugs and two leads – in fact it is only superficially different from a regular set of probes in that both plugs are moulded from the same piece of plastic. The trick is that the multimeter’s input sockets have split contacts that allow all four wires to be connected with just two plugs. The TL705 leads contain a pair co-axial wires connected to copper-tipped Kelvin probes. So despite being able to use them like regular probes, measurements down to a few milliohms are possible in the 4-wire mode. The copper tips avoid any dissimilar metal junctions in the probes. Such junctions can act like thermocouples and bias voltage readings. Conclusion While the DMM4050 has a decent set of features, its focus is on precision. We can’t list all of the accuracy figures here but the data sheet, available from www.tek.com, has that information. In this sense, you get what you pay for – the measurement errors of this unit are much lower than cheaper 6½ digit multimeters. Many DMM4050 purchasers will also want to spend the extra for the TL705 4-wire test lead since it makes accurate resistance measurement so much easier and accuracy is this unit’s forte. Availability The DMM4050 with a standard three-year warranty is available from TekMark for AU$1885 plus GST and delivery. The DMM4040 (without capacitance or temperature mode) is AU$1531 plus GST. The 5.5 digit DMM4020 is AU$1044.00 plus GST. To contact TekMark, e-mail enquiries<at>tekmarkgroup.com or call (02) 9911 3888. Further details are at www.tekmarkgroup.com/au SC Issues Getting Dog-Eared? Are your SILICON CHIP copies getting damaged or dog-eared just lying around in a cupboard or on a shelf? Can you quickly find a particular issue that you need to refer to? REAL VALUE AT $14.95 PLUS P & P Keep your copies of SILICON CHIP safe, secure and always available with these handy binders Each binder holds a full year (12 issues) with simple wire springclips to hold them in. Just $A14.95 plus $10 p&p per order (includes GST). (Available in Australia only). To order, simply call (02) 9939 3295 with your credit card handy . . . or fill in the handy order form in this issue and fax it to (02) 9939 2648, or mail it to PO Box 139, Collaroy NSW 2097. siliconchip.com.au May 2010  81