M3 Electronix LCR Meter

The LCR Meter by M-Cubed Electronics is another very nice kit - IMHO - a must for every workbench. The kit is using very high quality components and PCBs. Included is a powder-coated aluminum case which gives the LCR Meter very professional look. This LCR Meter by itself has an enormous amount of features (all listed on their web site). There are also a few optional test fixtures available. The accuracy is impressive for a kit - basic accuracy of 0.2% using the supplied calibration resistors. The best part is the use of the "4-wire test method" which eliminates errors caused by the test leads and fixtures - a feature normally seen only in high-end test equipment. Upgrades of the firmware are done by sending the unit back to M-Cubed. There is a JTAG connector on the main PCB which allows for re-programing of the PIC but the firmware code is not made public. All SMD components (incl. the PIC) were pre-installed on the PCB along side with some other components, needed for the initial programing of the PIC (crystal oscilator, a few caps and the JTAG connector). The rest of the components were sorted by type in plastic bags. The assembly instructions are very clear and logical. The only gripe that I have is about the capacitors - some of them are small and on the top of this, some of the value markings were partially erased. Even with the help of my Zeiss-Winkel microscope I was unable to identify some of the caps just by looking at them. I had to use another LC meter to actually measure their values - this is not a problem if you have a LC meter handy but the irony is still there - you need a LC meter to build LC meter. Another small issue is the power connector - a male 5.5mm x 2.1mm barrel connector is not provided with the kit and you have to find one - I rather pay a little extra and get it with the kit instead of wasting time to look for the proper connector. Other than that, the assembly went very smooth over a couple of evenings.

This is the content of the kit right out the box. Calibration resistors are also provided with the kit. The basic kit comes with a probe made out of 4 Pomona-style clips - everything need to construct the probe is supplied with the kit.

These are the 4 boards - Input board, Keyboard board, Main PCB and LCD. Most of the resistors supplied with the kit are of the 1% tolerance type but there are also some 5%. I had plenty of 1% resistors in stock so I replaced pretty much all of the 5% resistors. This might not improve the accuracy a lot but at least the 1% (blue body) are metal-film type resistor with more stable values than 5% carbon-film type. The specified accuracy for the meter is between 0.2% and 0.8% when calibrated with the supplied 0.1% calibration resistors.

The PCBs are "sandwiched" together (using connectors and stand-offs) in the aluminum enclosure. 5-pin DIN connector (on the right) is used to connect the test probe or fixture. On-off switch and the power connector are wired on the left side. Very little space is wasted inside the enclosure and the PCBs are densely populated as well.

This is the finished meter. This meter is using the 4-wire probe method for measuring DUT (Device Under Test). 2 wires are supplying and measuring the AC (0.5Vrms) current thru the DUT and 2 other wires are measuring the voltage across the DUT. This allows for a very accurate measurement canceling out the error introduced by the probe. Furthermore, I increased the accuracy by calibrating the meter with my own 0.01% resistors instead of using the supplied 0.1% calibration kit. If an accurate Ohm-meter is available, the firmware allows for correction of the calibration values and then the supplied resistors can be used just as a "transfer" standard. On this picture high-current 270 uH inductor reads 263.8 uH.

During measurement, the display shows additional information such as the test frequency used for measurement (adjustable up to 15.6 kHz), the Auto-range mode, currently used range, test model (parallel or series), secondary value (ESR in this case) etc. Capacitor with marked value of 5.6 pF and tolerance 5% reads 5.56 pF. There is a menu option for the averaging mode - higher averaging results in more stable measured value. The test frequency is very low - only up to 15.6 kHz (there is an EU version with max freq. of 25 kHz) - not really RF range measurments but gives an idea.

The power supply for the meter should be between 9V-13V. Current draw is about 200 mA . Using the small 9V alkaline battery is out of question - it will last just a few minutes. The backlight can be switch off but the current is still too high for such battery. I am using 2.9Ah 12V SLA battery to power the meter.

This picture shows the inductance and Q for 330uH inductor in "series" model (Ls).

I built a few different sets of probes - Kelvin clips, 4-wire Pomona-style clips and SMD tweezers.
The Kelvin clips probe is the best all-around type. One half of each clip carries the Drive and the other half the Sense signal. It has the best accuracy for testing leaded components. The 4-wire clips probe is useful for testing transformers (there is a special mode for this), already installed components or using it with a small PCB fixture for quickly checking / sorting multiple components (there is a SORT mode alowing a tolerance value to be set and and audio beep indicating if the tested component is conforming or not). The SMD tweezers are a bit less accurate when measuring capacitors due to stray capacitance in the actual tweezers.