Fluke 116 has no fuses!? - Page 1
Forum section: electronics / beginners

author: smoothtalker
author_rank: Regular Contributor
timestamp: October 08, 2013, 04:02:50 pm
content: guys I'm not EE trained but just a hobbyist.May i know why is Fluke 116 not fused? I understand it only has a uA range. but wouldn't a faulty test subject or innocent user error cause an accident? that could kill someone!

author: AndreaEl
author_rank: Contributor
timestamp: October 08, 2013, 04:23:32 pm
content: There are another topic about Fluke 116 Fuse.I have a Fluke 115 and it have a 20A Fuse. But it have the 20A range.https://www.eevblog.com/forum/beginners/please-halp-me-understand-my-fluke-116/

author: AG6QR
author_rank: Frequent Contributor
timestamp: October 08, 2013, 04:28:07 pm
content: It has only high impedance input.A fuse is required for low impedance input, because large currents could flow, particularly if you put the meter across a stiff voltage source. Most meters have fuses on their terminals for something like a 10A or 400mA range.But the fluke 116 doesn't have a 10A or 400mA range. You can put the Fluke 116's probes across any voltage source with the meter on any setting, and the impedance of the meter itself prevents dangerous current from flowing.The 116's microamp range is very high impedance, which makes it all but worthless for doing something like measuring the current consumption of a very low power battery operated electronic device. But it's designed for HVAC field technicians. They use microamp range to measure the current from a flame sensor in a gas burning appliance. For this application, a high impedance microamp range is useful.

author: smoothtalker
author_rank: Regular Contributor
timestamp: October 08, 2013, 09:09:25 pm
content: Quote from: AndreaEl on October 08, 2013, 04:23:32 pmI see! So in essence there is no current flowing into that uA range at all? If that can be done, why doesn't those 10A multimeter function that way too? I'm not EE trained apologies for the question

author: Unknown
author_rank: Unknown
timestamp: October 08, 2013, 09:26:31 pm
content: Measuring 10 A requires 10 A to flow into the meter. If the burden voltage has to be limited to reasonable levels (say below 1 V), then the 10 A input needs to have a resistance of less than 0.1 ohm (I assume you understand Ohm's law, even without being an EE). If you then connect the leads across 240 V mains, then 2.4 kA could flow for a few milliseconds until the breaker trips. Assuming there is a breaker. This is why you need a fuse for 10 A. A high rupture current (HRC) fuse, since your standard 10 A fuse won't be able to interrupt that 2.4 kA.If you do the math for the uA range then you'll see the resistance can be much higher, limiting the maximum current even under overload conditions to much lower levels.

author: smoothtalker
author_rank: Regular Contributor
timestamp: October 08, 2013, 09:43:09 pm
content: Quote from: alm on October 08, 2013, 09:26:31 pmAhh I did some google on HRC fuse. So the main difference from nonHRC fuse is that it prevents arc over of current?And the reason why other fluke meters has fuse is due to low resistance so as to minimize burden voltage? But why can't those meters measure like how the 116 measures current? Isn't that safer? And no concerns for burden voltage

author: Nerull
author_rank: Frequent Contributor
timestamp: October 08, 2013, 09:47:40 pm
content: Because that would make it essentially useless. Imagine trying to power a standard 12V device with a 10MOhm resistor in the current path. You won't get any usable power at all, and any result you get won't resemble the result you will get without the multimeter in the circuit. An ideal multimeter is transparent - the circuit operates as if it wasn't there.The 116 is built for a very specific job and it isn't all that useful outside of it. The way it's current sensor works makes it useless for most electronics.

author: AG6QR
author_rank: Frequent Contributor
timestamp: October 08, 2013, 09:48:18 pm
content: Quote from: smoothtalker on October 08, 2013, 09:09:25 pmNo, the current measured by an ammeter always flows through the ammeter, regardless of the scale. Kirchoff's current law, combined with the way you hook up an ammeter, guarantees it to be so.The Fluke 116 can measure up to 600 uA.Many typical meters can measure up to 10A, or 16,666 times more current.The shunt resistance isn't strictly specified in either case, so that ratio of max scale readings isn't a very precise indicator of what kind of protection is required, or what kind of current spikes might happen if you stuck the probes directly into a wall socket. But as a rough order of magnitude, the Fluke 116 is dealing with less than one ten-thousandth of the current that a typical 10A meter handles. That's why the protection strategy can be different.QuoteThey DO measure current the same basic way. It's just that the currents are orders of magnitude higher on most meters, leading to orders of magnitude greater levels of power being dissipated in the meter. And burden voltage is always a concern (the 116's microamps range is nearly useless for general electronic purposes because of its high burden voltage).