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Fluke 381 review


Michael Collier
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I've been besting on a feature, and due to a bad ammeter in the genny, I got production to agree to a kit rental for a clamp meter. I took the opportunity to pick up a Fluke 381.

 

The obvious feature is the removable wireless display. It seems to be some sort of bluetooth/zigbee wireless scheme, ISM band so I assume it would work in other countries.

 

Anyway, I got it for the wireless feature, and it has really been a timesaver. I might be more critical about genny balance than others, but since I had no way of monitoring it, this has been a big help in making the balance simple.

 

most of the day I clamp onto the neutral just before the first distro, and keep the meter on my belt. While we light, I can take it out occasional and see how close I am. If the generator is in balance, it should read 0 amps. The more imbalanced, the higher the reading will climb. If it gets toward my safeline, I can check my hots with the meter (sadly I have to walk to distro for that) to find my low legs. The wireless feature comes in handy here because I can place it on the box and not have to contort myself to read a sideways meter clamped to a leg.

 

The distance is alright, our main stage is 150x100, and it can almost reach anywhere. It definitely can't be clipped at the generator and reach through concrete walls. They claim 10m, and I would say it's at least that, if not twice that in a stage environment.

 

The biggest problem from my perspective is the beep. It beeps when you hit one of the three buttons on the display (min/max, hold, and light). It will also beep while in min/max mode, when a new record is achieved (theoretically this would only happen during setups, by the time the take happens, the max would already be high). That said the beep is pretty quiet. I sometimes don't notice it myself, even during a quiet moment.

 

It runs off of 3 AAA's in the meter, and 2 in the display (for the price I would have liked to have seen rechargeable cells). It's a Fluke, so you can bet it's accurate, and it measures true RMS, instead of just-RMS (which is handy when you have a lot of electric ballasts running. It will measure the power factor loss and harmonic currents better than an RMS meter, which assumes a perfect sine wave and linear loads)

 

Also (and this is a simple reason to like a tool) I love the backlight they put in it. They are clean while LEDs (probably in the 5000K range.) The wash is even. It never blinds me when I am working in a dark corner, or seem too dim when walking taking readings in brighter areas.

 

At a 1000 amps, it will cover just about any power drop (at least for shows that don't have a genny op to help you out.) One thing I've wanted to try (but haven't had a chance yet) was to use the inrush feature to figure out the striking current of bigger HMIs.

 

Anyway, that's my impression of it. I need a good meter for other things, but I have been pretty happy with it.

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  • 4 years later...

Hey Michael,

 

I know this post is around four years old, but I'm looking to buy a fluke clamp meter and I was wondering what kinds of situations would require measuring hertz. You mentioned for HMI's? Also since I'm low on money how often do you find the DC capabilities coming in handy?

 

Thanks!

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I'm looking to buy a fluke clamp meter and I was wondering what kinds of situations would require measuring hertz. You mentioned for HMI's?

 

Since the advent of electronic HMI ballasts, measuring hertz is not as important as it was when HMI ballasts used magnetic ballasts. In those days you had to make sure the generator was spinning so that the frequency was +/- a quarter cycle of 60Hz (59.75-60.25Hz) to avoid flicker. By squaring off the waveform to the globe, electronic ballasts eliminate flicker except at very high speeds in which case you need to use 1000Hz high-speed ballasts.

 

If you will be using electronic HMI ballasts, you want to make sure you get a meter that reads true RMS. In an introductory workshop my local, IATSE Local 481, offers for set electrics we do an exercise where the students meter the voltage and current on a putt-putt generator (non-inverter type) while running a non-pfc 2.5kW HMI light. Since, invariably, the meters brought by the students range in quality, the readings they get range from being 84% over to 40% under what they should be. We then so the same exercise with tungsten lights and they all read the same. The discrepancy in the results is a good jumping off point for a discussion about how meters work and that they can be mislead by the distorted waveforms drawn by some electronic HMI and Kino ballasts. Since the consequences of under measurement can be significant - overloaded cables may go undetected, bus-bars and cables may overheat, fuses and circuit breakers will trip unexpectedly - it is important to understand how meters work and why only meters based on "true RMS " techniques should be used on power distribution systems supplying nonlinear loads. To see why that is the case use this link: http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorMeters

 

Guy Holt

ScreenLight & Grip

Lighting Rentals & Sales in Boston

Edited by Guy Holt
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  • 6 years later...
On 6/20/2015 at 8:06 AM, Guy Holt said:

 

Since the advent of electronic HMI ballasts, measuring hertz is not as important as it was when HMI ballasts used magnetic ballasts. In those days you had to make sure the generator was spinning so that the frequency was +/- a quarter cycle of 60Hz (59.75-60.25Hz) to avoid flicker. By squaring off the waveform to the globe, electronic ballasts eliminate flicker except at very high speeds in which case you need to use 1000Hz high-speed ballasts.

 

If you will be using electronic HMI ballasts, you want to make sure you get a meter that reads true RMS. In an introductory workshop my local, IATSE Local 481, offers for set electrics we do an exercise where the students meter the voltage and current on a putt-putt generator (non-inverter type) while running a non-pfc 2.5kW HMI light. Since, invariably, the meters brought by the students range in quality, the readings they get range from being 84% over to 40% under what they should be. We then so the same exercise with tungsten lights and they all read the same. The discrepancy in the results is a good jumping off point for a discussion about how meters work and that they can be mislead by the distorted waveforms drawn by some electronic HMI and Kino ballasts. Since the consequences of under measurement can be significant - overloaded cables may go undetected, bus-bars and cables may overheat, fuses and circuit breakers will trip unexpectedly - it is important to understand how meters work and why only meters based on "true RMS " techniques should be used on power distribution systems supplying nonlinear loads. To see why that is the case use this link: http://www.screenlightandgrip.com/html/emailnewsletter_generators.html#anchorMeters

 

Guy Holt

ScreenLight & Grip

Lighting Rentals & Sales in Boston

What particular True RMS meter would you recommend, Guy?

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