Multimeter Review - Fluke 233

I have been using the Fluke 233 for a few weeks now, so it feels like a good time to publish an update. Overall, there is no doubt that the Fluke 233 is a really good piece of kit, but one or two minor annoyances have appeared. For all that Fluke price themselves near the top of the market, there are signs that accountants and marketing executives have had a say in things. More about that later.

To set the tone, I present a photograph of two Fluke hand held multimeters, produced around twenty years apart, and connected to a common bench power supply.

That is a difference of 0.1%. In twenty years. I can appreciate that a cheap meter purchased today may be trimmed to that level of accuracy, but I really don’t think they will be that close in five years time let alone twenty. The old Fluke 77 hasn’t had an easy life either. Overvolts, overcurrent, moisture, cold, heat, concrete floors. You name it. It is an interesting point to note that it still has the desk stand intact, despite being rather frail looking.

I could copy a table of measurement comparisons, but there is really no need to. The photo above sums it up really; volts, amps, ohms - all absolutely spot-on. I don’t have lab grade references, just a few 0.1% resistors, an Analog Devices voltage reference I hacked together, and of course other meters. For all these test restrictions, the real world accuracy of the Fluke 233 is clearly better than that specified in the sales literature and user guide.

It does seem disproportionate to spend such a small amount of space writing about how good a meter it is, but there you have it. A damn good reliable meter, designed not to be replaced after 2 years. It has already earned a permanent place on my desk.

It seems churlish to pick out the bad points from what is clearly such a good piece of kit. But I feel it is only fair to prospective purchasers that I cover certain limitations and problems.

First of all, as I mentioned in my initial review, charging £43 for a Chinese made soft woven nylon carry case is ridiculous. Heck, that is £2 more than a set of decent Fluke test probes. Which reminds me, the probes supplied are okay, but no more than that. I would expect probes like these to be supplied with a £100 meter. Testing them in the ‘fridge, they don’t appear to be low-temperature flexible ones with silicone insulation. Have some pride in your products Fluke! It is like buying a BMW M5, only to find they have supplied it with Korean ditchfinder tyres. Details really matter.

I guess Fluke rely on people buying accessories through department budgets. With the US and European economies in the state they are, people will be looking for better value from their products, and Fluke could do worse than to take a look at their bundled accessories.

AVO and Beyond

Beyond the usual amps / volts / ohms,  what do we have? Well, I am afraid this is where the marketing execs strike.

The Annoyances.

Diodes. The diode test reads up to 2 Volts, which is fine for diodes and most LEDs, but not for blue, UV or “white” hybrids currently replacing filament lamps by their million. The unit has 4.5V available to it directly from the batteries without any boost (and minus any lost from the constant current circuit), I’m sure they could and should do better than 2V.

Capacitance. Useful for doing some general checks, but a resolution of 1nF isn’t going to cut it with radio frequency, or even audio circuits, and a maximum of 10,000uF is way below the values used in many conventional linear power supplies. They seem to have forgotten that old technology still exists and needs repairing. I can understand not going down to the pF level in a meter like this, but it should measure to 100,000uF. As with all the ranges though, accuracy looks to be spot on.

Frequency measurement. A maximum stated frequency of 50kHz (although people have measured up to around 100kHz). Given that small switched mode PSUs often run up to 4MHz, 50kHz is going to limit the meter’s usability. Somewhat of a “tacked-on” facility I feel.

Batteries.  400 hours estimated life is excellent. That probably works out at 3 to 4 years usage for me. But, when they go, it does mean potentially 5 batteries have to be replaced. Would it not have been better to integrate a small rechargeable battery in the head unit, and charge it via two direct contacts? Sufficient capacity for 5 hours running should be plenty. Mounting stainless contacts in the runners would allow them to stay clean. Battery life should not be compromised as there would be no need to run an I/R sender.

Missing in Action:

Zeroing. Despite having a Max/Min/Average facility, there is no zeroing function! I’m sure it must be a relatively trivial job to add this to the firmware. It isn’t vital by any means, but adding it would need no more hardware. I wonder if marketing people made the engineers remove this facility?

Duty ratio. Again, this surely cannot be a difficult function to add, and it is one that is essential to anyone dealing with automotive development and repair. I guess they want you to buy a more specialised meter – but that one wouldn’t have the removable display, which is so useful in the auto market.

Millivolts. I feel rather churlish mentioning it, but 0.1mV feels rather coarse for a modern meter.

Conclusion:

I don’t want to mislead the reader, none of these are killer problems in any way, but most of them could have been removed or mitigated. You might think a meter with all my requested modifications would start to encroach on Fluke’s top line portable multimeters, but they have 20,000 and 50,000 count displays and a minimum of double the measurement accuracy. Surely that would be enough clear water. None of these problems stop the 233 being a seriously good multimeter that I will probably still be using in another 20 years.

Headless Meters Are The Future

I have the suspicion that, before long, most multimeter ranges are going to offer a ‘headless’ option. I wasn’t sure how useful I would find it, but in reality I have already used it several times in situations that would normally have involved messy extension wires.  Having said that, I am still a bit puzzled at who the Fluke 233 is targeted at. If you need a remote display meter then there is no choice. It has to be the 233. If you don’t, then go for Fluke’s 175 and save yourself £70. Personally I would pay a little more and go for the 287, which is what I think the marketing people want you to do. In my case, I already have a nice little space on my desk reserved for a 287. All I have to do is save up for it - hopefully it will not be 20 years this time!

Mike