I am working on guitar effect boxes and would like a DMM that has resolution to the nanoamp for measuring base and collector current being fed to transistors. I am often finding current values in the 100 to 200 nanoamp range and need to be able to evaluate them to something finer than .1 microamp in order to determine proper gain values. Would prefer something not out of hobbyist's price range. Bench or hand held is not an important factor.
If anyone knows of any particular meters that would fit this bill or can point me to source material your help is greatly appreciated.
If anyone knows of any particular meters that would fit this bill or can point me to source material your help is greatly appreciated.
Just of curiosity I need to ask, what are you using today in such measurements?
No one can offer a suggestion about a better meter with out been aware of what you use now.
No one can offer a suggestion about a better meter with out been aware of what you use now.
I currently use a pair of handheld Extech MN36 meters, one tied into the base current and one tied into the collector current. The best resolution I get is to 0.1uA. Unfortunately, that is not fine grained enough for the very low current values I am encountering, i.e. between 0.1uA and 0.2uA.
Resolution below .1uA is not available in common handheld meters because it requires either too high of a shunt resistance to be practical or an extra DC precise amplifier with tons of gain. If you want to make a nanoammeter yourself, those are still the options.
You don't need a new multimeter, you just need this:
The uCurrent Gold. It's designed and sold by Dave Jones at EEVBlog and is a current to voltage converter. It has a nA, uA and mA range. Not only will it allow you to measure nA currents, it also has a much lower burden voltage than pretty much all multimeters. This is especially important with dealing with nA currents. You basically use this in conjunction with your regular multimeter on the mV range and the reading in mV is the current in mA.
The uCurrent Gold. It's designed and sold by Dave Jones at EEVBlog and is a current to voltage converter. It has a nA, uA and mA range. Not only will it allow you to measure nA currents, it also has a much lower burden voltage than pretty much all multimeters. This is especially important with dealing with nA currents. You basically use this in conjunction with your regular multimeter on the mV range and the reading in mV is the current in mA.
The pile of complains is large by the ones who got it.
I do not have to offer an alternative solution, by neither I would trust, something which is not accepted for verification by any calibration lab.
Try a Keithley 2001.
Range Resolution
200 uA 10 pA
2 mA 100 pA
20 mA 1 nA
200 mA 10 nA
2 A 100 nA
Maybe a Keithley 2000 will be ok also?
Range Resolution
200 uA 10 pA
2 mA 100 pA
20 mA 1 nA
200 mA 10 nA
2 A 100 nA
Maybe a Keithley 2000 will be ok also?
Measuring low currents? -- read up on the application notes at Linear Tech, and Bob Pease (RIP) "What's all this fempto-Ampere stuff anyway?" which is archived on the Texas Instruments site.
My Fluke 177 has a DC millivolt range, but below 5mv it gets a bit wonky. You'll need a very low noise, low bias current instrumentation amplifier, perhaps an OPA4140 arranged as an inamp with a gain of 10,000, perhaps you can get away with a shunt resistor of as much as 100R -- then 10nA will read 10mV. For this low current, low noise measurement you will need to use shielded twisted pair, run the INAMP off 9V batteries which are decoupled with 100nF ceramic caps, etc., etc. It can be done for less than $10.
EDIT - specifically look for application note #105 of Linear's website.
My Fluke 177 has a DC millivolt range, but below 5mv it gets a bit wonky. You'll need a very low noise, low bias current instrumentation amplifier, perhaps an OPA4140 arranged as an inamp with a gain of 10,000, perhaps you can get away with a shunt resistor of as much as 100R -- then 10nA will read 10mV. For this low current, low noise measurement you will need to use shielded twisted pair, run the INAMP off 9V batteries which are decoupled with 100nF ceramic caps, etc., etc. It can be done for less than $10.
EDIT - specifically look for application note #105 of Linear's website.
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The gain of a properly designed transistor circuit is determined by external components. You can measure the health and approximate current amplification factor of a transistor by a Beta-tester, part of most hand held DMMs.
You can use a 10k resistor as sense element and a "zero drift" instrumentation amplifier (e.g. INA333), configured to 100x gain. This gives nA readings in the mV range of your DMM, or uA readings in the V range.
Samuel
Samuel
Dave Jones's uCurrent, linked in an earlier post, uses this strategy. However instead of the INA333 (10uV input offset voltage, typ; 25uV max), Dave chose the MAX4239 (0.1 uV input offset voltage, typ; 2uV max) and operates it in a single opamp topology.
It's well known that you and Dave don't get along. I have known dozens of people that received uCurrents without issue. The only issues I have seen on his forum are for a couple of bad switches. He took care of those immediately. So as for the long lists, I strongly doubt they exist.
Most cal labs won't touch anything not made from one of the major manufacturers. I've found this out personally, so acting like its some sort of statement of quality, instead of the fact there are only a small number of devices, is just misleading.
Yep, I agree. If you don't want to purchase the uCurrent you can build something similar yourself.
The fastest handheld of our times at 1mV AC/DC is the DER EE DE-208A, with Agilent U-1272A far behind as it needs 3-4 seconds to settle.
Even FLUKE 28II starts measuring at above 3-4mV at AC
For your information I have no problem at all about communicating with the man, and we do that due Twitter.
When mentioned to him that his design needs inspection and approval in order to become an commercial solution, he stayed silent.
Behind the test and measurement equipment industry there is hidden the scientific community and engineers of the best universities world wide.
If I have to choose a pal ? I choose them.
There is a very cheap and simple solution to that problem, and I'm surprised no one cared to mention it: any basic multimeter has an inherent capability of measuring 20nA full scale.
The 200mV range, with its 10MΩ resistance provides just that, and if that is too sensitive, just add a parallel resistor: with 1.111MΩ, it will become 200nA, etc.
Now that is only applicable to a basic, battery-operated DMM: as soon as you opt for something interfaceable, USB or anything else, or even just something that is mains-powered, issues will show up, and more deterministic solutions will be required, but with a completely floating and battery-powered instrument, very reliable measurements can be obtained in this way at very little cost.
If 20nA is not sensitive enough, many "upper class" DMM's have the option of disabling the internal 10MΩ resistance for the first (or the two first) voltage ranges: you can then use your own shunt resistor.
The downside of these methods is the voltage drop: 200mV full range. It has to be seen in perspective: it is exactly the same drop as for regular current ranges, and you can use use only part of this range, or use a 20K pts DMM, which is quite cheap nowadays.
To summarize, if just a numerical value is required, no recording, etc, then the cheap standalone DMM option is the best
The 200mV range, with its 10MΩ resistance provides just that, and if that is too sensitive, just add a parallel resistor: with 1.111MΩ, it will become 200nA, etc.
Now that is only applicable to a basic, battery-operated DMM: as soon as you opt for something interfaceable, USB or anything else, or even just something that is mains-powered, issues will show up, and more deterministic solutions will be required, but with a completely floating and battery-powered instrument, very reliable measurements can be obtained in this way at very little cost.
If 20nA is not sensitive enough, many "upper class" DMM's have the option of disabling the internal 10MΩ resistance for the first (or the two first) voltage ranges: you can then use your own shunt resistor.
The downside of these methods is the voltage drop: 200mV full range. It has to be seen in perspective: it is exactly the same drop as for regular current ranges, and you can use use only part of this range, or use a 20K pts DMM, which is quite cheap nowadays.
To summarize, if just a numerical value is required, no recording, etc, then the cheap standalone DMM option is the best
My old Fluke 867 can do .01uA res with a 100 ohm loading (builtin togglable setting) or milliamp range with a 1 ohm load. Scale range 300uA or 30ma respectively.
I took a look at a Canadian Fluke site and couldn't find any of those numbers. There was, however, a desktop multimeter that looks like it should fill my needs and some, the 8808A.
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