Kit review – High Accuracy LC Meter

Hello readers

Time for another kit review. Lately one of my goals has been to make life easier and in doing so having some decent test equipment. One challenge of meeting that goal is (naturally) keeping the cost of things down to a reasonable level. Unfortunately my eyesight is not the best so I cannot read small capacitor markings – which makes a capacitance meter necessary. Although I have that function within my multimeter, it is often required to read resistors in the same work session.

Thus the reason for this kit review. A day trip to Altronics saw me return with (amongst other things) their High Precision LC Meter kit. The details were originally published in the May 2008 issue of Australia’s Silicon Chip magazine. The meter specifications are:

  • Capacitance – 0.1pF to over 800 nF with four-digit resolution;
  • Inductance – 10 nH to over 70 mH with four-digit resolution;
  • Accuracy of better than +/- 1% of the reading;
  • Automatic range selection, however only non-polarised capacitors can be measured.

The power drain is quite low,  between 8 (measurement) and 17 milliamps (calibration). Using a fresh 9V alkaline battery you should realise around fifty to sixty hours of continuous use. At this point some of you may be wondering if it is cheaper to purchase an LC meter or make your own. A quick search found the BK Precision 875B LCR meter with the same C range and a worse L range for over twice the price of the kit. Although we don’t have resistance measurement in our kit, if you are building this you already have a multimeter. So not bad value at all. And you can say you built it :)

Speaking of building, assembly time was just under two hours, and the kit itself is very well produced. The packaging was the typical retail bag:

retailkitss

The first thing that grabs your attention is the housing. It is a genuine, made in the US Hammond enclosure – and has all the required holes and LCD area punched out, so you don’t need to do any drilling at all:

hammondcasess

The enclosure has nice non-slip rubberised edging (the grey area) and also allows for a 9V battery to be housed securely. The team at Altronics have done a great job in redesigning the kit for this enclosure, much more attractive than the magazine version. The PCB is solder-masked and silk-screened to fine standard:

pcbss2

There are two small boards to cut and file off from the main PCB. We will examine them later in the article. All required parts for completion were included, and it is good to see 1% resistors and an IC socket for the microcontroller:

partsss1

At first I was a little disappointed to not have a backlit LCD module, however considering the meter is to be battery operated (however there is a DC socket for a plugpack) and you wouldn’t really be using this in the dark, a backlight wouldn’t be necessary. Construction was easy enough, the layout on the PCB is well labelled, and plenty of space between pins. Lately I have started using a lead-former, and can highly recommend the use of one:

leadformerss

Assembly was quite simple, just start with the lower profile components:

assemble1ss

 

… then mount the LCD and the larger components:

assemble2ss

… the switches and others – and we’re done:

finishedsolderingss

The only problem at this point was the PCB holes for the selector switch, one hole was around 1mm from where it needed to be. Instead of drilling out the hole, it was easier to just bend up the legs of the switch and keep going:

switchlegsss

At this stage one has to cut out two supports from the enclosure, which can be done easily. Then insert the PCB and solder to the sockets and power (9V battery snap). Initial testing was successful (after adjusting the LCD contrast…

inittestss

If you look at the area of PCB between the battery and the left-hand screw there are eight pins – these are four pairs of inputs used to help calibrate and check operation of the meter. For example, by placing a jumper over a pair you can display the oscillator frequency at various stages:

calibrationss

Furthermore, those links can also be used to fine-tune the meter. For example one can increase or decrease the scaling factor and the settings are then stored in the EEPROM within the microcontroller. However my example seemed ok from the start, so it was time to seal up the enclosure and get testing. Starting with a ceramic capacitor, the lowest value in stock:

3p9pfss

Spot-on. That was a good start, however trying to bend the leads to match the binding posts was somewhat inconvenient, so I cut up some leads and fitted crocodile clips on the end. The meter’s zero button allows you to reset the measurement back to zero after attaching the leads, so stray capacitance can be taken into account.

Next, time to check the measurement with something more accurate, a 1% tolerance silvered-mica 100 picofarad capacitor:

99pfss

Again, the meter came through right on specification. My apologies to those looking for inductor tests – I don’t have any in stock to try out. If you are really curious I could be persuaded to order some in, however as the capacitance measurement has been successful I am confident the inductance measurement would also fall within the meter’s specifications.

As shown earlier, there were two smaller PCBs included:

pcbadaptorsss

The top PCB is a shorting bar used to help zero the inductance reading, and the lower PCB is used to help measure smaller capacitors and also SMD units. A nice finishing touch that adds value to the meter. The only optional extra to consider would be a set of short leads with clips or probes to make measurement physically easier.

When reading this kit review it may appear to be somewhat positive and not critical at all. However it really is a  good instrument, considering the accuracy, price, and enjoyment from doing it yourself. It was interesting, easy to build, and will be very useful now and in the future. So if you are in the market for an LC meter, and don’t mind some work – you should add this kit to your checklist for consideration. It is available from Altronics stores and resellers.

In the meanwhile have fun and keep checking into tronixstuff.com. Why not follow things on twitterGoogle+, subscribe  for email updates or RSS using the links on the right-hand column? And join our friendly Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other –  and we can all learn something.

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John Boxall

Founder, owner and managing editor of tronixstuff.com.

18 Responses to “Kit review – High Accuracy LC Meter”

  1. Lokhin says:

    LC metr очень практичен. Выполняет в высоком % измерения и удобен в производстве ремонта. Большое спасибо за предоставленный обзор. Имею желание пользоваться.

  2. noozillander says:

    Thanks for the great review John. Much appreciated.
    Have just bought this kit in NZ, on the basis of your review.

  3. David Bradley says:

    Hi John great article have bought kit from Alltronics,looking forward to build,wondered where you got your lead former ,many thanks Dave

  4. Rapsod says:

    Where did you get lead-former tool?

  5. Steve May says:

    Hi John,
    Thanks for the kind review.
    We also like the way the kit turned out in the hammond case.
    The problem with the switch holes will be looked at and addressed.
    On your recommendation we will also include one of our banana plug to crocodile clip leads in future runs of the Kit.
    Thanks again.
    The Team @ Altronics

    • John Boxall says:

      Hello Steve
      Thank you for reading and taking note of the review points, it’s great to know that a local company is listening and cares about such things :)
      Keep up the great work
      cheers
      john

  6. Juliean says:

    Anyone know of a US retailer for these?

    • John Boxall says:

      Altronics is an Australian company who produces the kit. They should be able to export one to you. If not, I can do this for you at cost if you like.
      Cheers
      john

      • Juliean says:

        I’m sure they can do it, was hoping to avoid dealing with international shipping. Will probably email them to see if they have us retailers, was just hoping someone might know off hand.

  7. Ben says:

    Can you tell us what the test frequency is? Most L meters do not test at audio frequencies and are thus not suitable for measuring inductances in audio equipment and electronic instruments.

    • John Boxall says:

      I’m between houses so it’s in storage with the documentation for a few more weeks so I can’t look it up. The internet didn’t come up with the answer either. Perhaps ask the Altronics kit department via here – http://www.altronics.com.au/index.asp?area=cont
      john

    • Brett says:

      Hi Ben,

      The meter sets up an LC circuit with internal reference components and the part under test.
      This is what gives the meter its accuracy, It leaves the frequency as the measured variable that changes with the value of the part under test.

      The equations for the operating frequency are in the instruciton manual.
      Measuring very small values of capacitor, the frequency can be as high as 160KHz
      Measuring a 10uF cap, that falls to 5KHz.

      Kit Manager,
      Altronics.

      • Ben says:

        Thanks Brett!

        The problem is my Fluke 115 is a great multimeter, except when it comes to measuring nano- and picofarad-range capacitors or an inductor (no L measuring ability). Which is the reason I purchased an “L/C” meter kit a couple years back. You can imagine how disappointed I was to discover that it was only accurate measuring L in the MHz range (suitable only for RF work).

        What I would need to see the Altronics meter do is accurately measure the inductance of some known value inductor that would be used in audio, such as a 2.5mH inductor you might find in a speaker crossover. Or the L of a guitar pickup, or a tube plate choke (reactor); something of that nature.

        What I don’t need is a *third* capacitance meter.

        Best to you,
        Ben

  8. Ray Miller says:

    Very profession kit but had some problems with the reference oscillator stopping sometimes, C3 (especially) and C9 10uF capacitors both need to be low Z at 600kHz using either tantalum or low ESR electrolytic fixes the problem. On the battery side I substituted for REG1 7805 a LDO regulator LP2905ACX and the battery current dropped to <3ma (from about 20ma), simple cheap and significant battery saving.
    Cheers Ray

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