As discussed earlier in the month, I have a brand new Agilent 34461A benchtop digital multimeter. I have plenty of test leads (most silicone-insulated), but am in need of a good current clamp.
There are plenty of current clamp meters available, but I need a clamp with test leads that could be connected to my multimeter.
Note: This is a long post discussing my selection process for a multimeter-compatible current clamp. The post is not a general discussion, as it specifically details my step-by-step evaluation of two products, based on their specs, for particular needs.
Current Measurement Range: 50 mA to 15 A (ideal), or 200 mA to 15 A
Conductor Clamping Capacity: The clamp must fit my Extech AC line splitter, which has ~5/8″ square sides and ~0.725″ (~18.5 mm) diagonal dimensions.
Must be non-destructive, meaning it must work without interrupting the wiring or housing of the device under test.
Data-logging abilities, which is why I’m looking for a current clamp that can be connected to my multimeter, and not a standalone clamp meter.
Must have standard banana jack terminals, or work with an appropriate adapter.
I intend to use the current clamp meter to measure the power draw of corded power tools, such as drills, saws, sanders, and oscillating multi-tools.
Potentially, I might present such data in ToolGuyd reviews or product discussions, and so data logging and visualization is important. Using my Agilent 34461A multimeter would provide for easier workflow and data analysis, but I am not opposed to using another meter if there are clear benefits to do so.
Product Selection Approach
Given my intended usage, I quickly found two current clamps that looked like they could work – Fluke’s i30 and i200 clamps.
I then considered both products in the context of the technical specification I was most interested in – their current measurement ranges. After that, the decision-making process became choppy as I went back and forth between products.
Several times I was sure I knew which clamp would be best for my application, only to find new factors to take into consideration.
First I thought the i30 to be ideal, then the i200, then the i30 again. Ultimately, it seems like an i200 and i30, or two i30’s would be ideal. My current plan is to try a single i30 and evaluate the situation from there.
My approach was a little choppy, and it might have been different if I considered and compared more technical specifications early on. But, as you’ll see from the following discussion, the limitations and compromises of both products weren’t clear to me until I put a lot more time into thinking about which of the two short-listed products would be best for my needs.
I really thought that an A vs. B comparison would be quick and easy, but it turned out that wasn’t the case. My decision-making process could have been shorter, but that’s easy to say in hindsight.
Price: $440 via Amazon
The i30 measures current using a Hall Effect sensor, and can measure AC and DC currents. It does require its own 9V battery power, and has a ~30-hour runtime. The i30 measures current with high accuracy: ± 1% plus ± 2 mA.
It has a current measurement range of 30 mA to 30 A DC and 30m A to 20 A AC. The jaws can clamp onto a maximum conductor size of 19 mm, so it should work with my Extech line splitter.
Price: $128 via Amazon
The i200 uses more common electromagnetic induction methods to measure current, and so it can only measure AC current, where the current changes direction based on ~60 Hz frequency.
Right now I don’t anticipate needing to measure DC currents nondestructively, and so AC vs. AC/DC measurement capabilities is not a big concern.
What I am concerned about is the i200’s 0.5 A to 200 A measurement range. The lowest current it can measure is 500 mA, which is an order of magnitude higher than I was looking for. The i200 can clamp onto conductors as large as 20 mm in diameter.
Here’s Where Things Get Tricky
Most common AC line splitters have 1X and 10X loops. The 10X work contains multiple wiring loops in order to improve the resolution of the clamp meter or current clamp measurement. That is, a 1.00 A current draw will be measured as 1.00 A via the 1X loop areas, and 10.0 A via the 10X loop areas.
On first glance, the i30 seems most suitable for my application, as it can measure down to 30 mA, while the i200 can only measure down to 500 mA.
However, placing the i200 clamp around the 10X loop of my line splitter should allow the i200 to measure down to about 50 mA. A 15 A current will be measured as 150 A, which is within the i200’s rated current range (0.5 A to 200 A).
But then I looked at the current clamps’ outputs.
The i30 Hall Effect current clamp outputs 100 mV for every 1A of measured current. The i200 current clamp outputs 1 mA for every 1A of measured current.
My multimeter can measure down to 100 µA and up to 10 A, and down to 100 mV AC or DC.
With a 500 mA current draw and the 1X loop, the i30 will output 50 mV, and the i200 will output 500 µA (0.5 mA). My meter cannot measure below 100 mV, so the 10X loop would have to be used.
The same 500 mA current draw will look like a 5.0 A current draw with the current clamps fixed on the 10X loop, and would result in a 500 mV output with the i30 and 5 mA output with the i200.
Ideally, I would like to measure down to 50 mA.
Considering a 100 mA current draw and 10X line splitter loop, resulting in a 1.0 A measurement, the i30 would output 100 mV, and the i200 1 mA.
The practical current measurement limit of the i30 is therefore going to be 100 mA, if using the 10X loop on my splitter, while the i200’s limit will be 50 mA. The i30 can measure lower currents as low as 30 mA, but its output becomes unusably low. The i200, on the other hand, would be limited by its 0.5 A minimum measurement limit.
If the i30 is clamped onto the 10X loop of my line splitter, such that measurements below 1 A are amplified to produce outputs greater than 100 mV, the higher-end of the current measurement range drops to 2.0 A AC, as 2.0 A would be measured as 20 A.
In other words, if I want to use the i30, its usable range with my line splitter and multimeter becomes 100 mA to 2.0 A AC. That’s just not acceptable.
Walking into the comparison, I thought the i30 would be better for my needs, but that might not be the case. The i200 now looks to be the better choice.
So then I looked more closely at the i200’s accuracy.
My only concern now is about the i200’s accuracy, which is said to be ≤3% + 0.5 A in the 0.5 A to 10A range. In other words, low-current measurements are going to be highly accurate. To minimize that 0.5 A part of the error, I would have to use the 10X loop of my line splitter all the time.
To my understanding, this means that a 1.0 A current draw, measured as 10 A via the 10X line splitter, would be measured with an accuracy of 3% + 0.5 A, or ± 0.8 A.
If sensing a 250 mA current via the 10X line splitter loop, the i200 would measure 2.5 A plus or minus 0.575 A, or 23%, which is a huge error. It means that instead of 2.5 A, the reading could be as low as 1.925 A or as high as 3.075 A.
I couldn’t get through to my friendly PR and test and measure expert contact at Fluke, so I tried Fluke’s customer service. Fluke doesn’t actually have an easy-to-find email address, so I called their industrial products selection and technical support phone number (1-800-44-FLUKE).
I spoke with Whitney, a Fluke product and applications expert, for about 12 minutes, and learned a few things:
The accuracy of the i200 is going to be a percentage PLUS that 0.5 A uncertainty. The 0.5 A accuracy figure is NOT a constant offset due to induction losses as I had hoped for.
The i30 can actually measure beyond 20V AC, up to around 30V AC, and has an overload capacity of 500 A. This is also provided in the manual, but I failed to notice these specs previously.
Some Fluke meters can measure below 100 mV, such as the 287 industrial data-logging meter, but I was really hoping to find something that works well with my Agilent.
I also learned that Fluke’s product and applications experts are very friendly and very knowledgeable. Whitney was unsure about one specification – the 287’s minimum voltage measurement limit (50 mV AC/DC) – but was able to pull it up lickity-split. I was really impressed with quality and speed of the discussion.
Soo… I Might Need Two Current Clamps
It actually looks like I might have to buy TWO current clamps.
When fixed onto the 10X loop of my line splitter, the i30 could measure current draw of about 100 mA to 2.0 A. It could potentially measure current draw as high as 3.0 A, but that’s still a bit low.
The i200, on the other hand, also via the 10X line splitter loop, would have ± 8% accuracy at 1.0 A (10 A sensed) and increase for lower current measurements. The effect of the 0.5 A accuracy component is thus reduced for higher current measurements. A 2.0 A current draw, which should be measured as 20 A via the 10X loop, would have an accuracy of ≤2.5% + 0.5 A (as per 10 A to 40 A specs), or a total of 5.0%. I could probably live with that, but lower would be better.
If I knew the current draw range would not go below 1.0 A, then the i30 could be used exclusively, on the 1X loop, where it could measure well past the 15 A maximum current measurement limit I’m looking for.
But if I want to accurately measure the FULL range, from say 500 mA or less (down to 100 mA) and up to 15 A, I would have to use TWO sensors simultaneously. Either an i30 and an i200, or two i30s would be needed.
Moving the i30 from the 10X loop to the 1X loop of a line splitter back and forth during testing is not an option. So the only feasible means is to use two clamps and to combine the logged data together.
It would be more economical to use one i30 and one i200 current clamps, but two i30’s would make it easier to combine data without having to worry about introducing additional sources of error into the mix.
One i30 could be on the 1X loop, and the other i30 on the 10X loop. Then, assuming the data matches up, one or more crossover points could be selected as needed.
The final data would include measurements from both clamps and would allow for measurements anywhere in the 100 mA to 15 A range. While I wouldn’t be able to measure down to 50 mA with my meter or without additional accessories, 0.1 A to 15 A with ± 1% plus 2 mA accuracy would be acceptable.
Sorry I wasn’t there for you, Stuart! Whitney does a great job, very glad she could help. Love your thinking process here – clamp output is tricky.
Don’t be sorry it was a good experience. =) Besides, this was a good opportunity for me to test Fluke’s technical support team.
If you are only measuring corded tools, you might be better off with something like this.
I did’t see the data logging requirement…I take my last post back lol
Those devices are designed to measure cummulative power draw.
I want to measure instantaneous current draw. It’s not about how much power is drawn over 1 hour or 1 day, but how the power draw changes, such as when a power tool goes from under no load to under a load.
Stuart – have you looked at some of Fluke’s other product – I have used a bunch of their larger i2000’s for current logging – they have been great – may be overkill but seems like they may work better for you?
The i2000 could lead to resolution issues at the low end.
In the 20A range, the i2000 Flex outputs 100 mV per A, which means I wouldn’t be able to measure anything lower than 1 A. Its accuracy is better than the i200, however, making it a better option than that one.
If I use the i2000 Flex with the 10X line splitter loop, I would be able to measure down to 100 mA as with the i30, but the measurement ceiling would also be 2.0 A, as this current would be measured as 20 A.
I looked at some of the other products as well, such as the Fluke 80i-110s and 90i-610s, and Tektronix A621 and A622 current probes. The 80i-110 and A622 have clamps that are too small, and the 90i-610s has high inherent error (2% plus 1 A) and its output is too small (10 mV/A). The Tektronix A621 is overkill, with its 2000 A max input current, but might be suitable.
I could potentially use my oscilloscope with the i2000 Flex, or Tek A621 sensors, but if going down that route then there would be no issue using the i30s (BNC version) in the same manner.