Road Test: FLUKE 190-204, SCOPE-METER
First, the grade for the FLUKE 190 Portable Scope-Meter; I give it an 8 out of 10. I would have given it a higher grade except for two reasons. First, the screen can’t seem to provide essential data on the current points per division and points per unit time, which is critical in understanding whether or not you’re looking at undersampled data (artifact) or not. The second reason is that they made it difficult and expensive to get the data points for a scope screen into a form that can be used in Excel or Matlab or other math programs. The scope itself although having limited math capabilities built-in is ineffective due to only having a capability of 3 significant figures. However, in its defense, these capabilities are more in-line with a lab scope than a portable.
This was a very enjoyable Road Test as I’ve used many brands and models of digital scopes yet I’d never had the chance to use a true portable digital scope, battery-operated and all. When I got the package delivered I had no idea what it was. It certainly seemed to be too big to be a potable scope. But to my surprise, that’s exactly what I got. The reason it was so big is that it comes with a heavy-duty case the size of a attaché case with locking clasps. The case is roughly 18.5” x 13 “ x 5” and weighs about 15.5 pounds. It offers significant protection from being dropped, being opened, or having something heavy hit it during travelling.
There are three compartments. The top is for paperwork, the middle is for the four identical (except for color coding) scope probes, and the bottom has separate compartments with the left-side for the USB cable and perhaps a USB memory stick (sold separately), the center stores the scope itself, and the right-side holds the power supply.
Speaking of the power supply, it has a black-box in the middle with cords for the 120 VAC 2-wire plug (other worldwide utility voltages available) and for the usual round type of plug with a female center. Being a portable unit, they thankfully thought ahead and made the overall length of the cords from end-to-end of about 14 feet, which is more than adequate for most needs in the field. I did find the power supply to be a bit underpowered as it takes at least five hours to fully charge the Li-ion battery, which gives up to 7 hours of usage time. However, to mitigate the problem of needing more than 7 hours on batteries, the battery is easily replaceable with another spare (sold separately) that can be replaced by a half-twist on two screws in the back to open the battery compartment and simply remove the drained battery and pop-in a fully charged one.
The Scope itself is actually considered a Scope-Meter as it can perform both functions to some degree. It’s not a full digital lab scope and it’s also not a full DMM. For example, it has no Ohmmeter function. It does have a current-probe accessory (sold separately) that can allow the user to either see current waveforms, use the meter function to measure current as: AC RMS, DC, AC+DC (TrueRMS), and along with a voltage reading on another of the 4-channels, it can give you automatic true power, reactive power, and more by doing point-to-point multiplication or other math on the signals which the user can either see on the scope, on see in numeric form like a DMM, or even both at the same time. The DMM feature I liked the least is that the user doesn’t even get a 3&1/2 digit output, let alone a 4&1/2 or more, but a paltry 3 digit output with marginal accuracy. For example, measuring an RMS or TrueRMS signal, the accuracy from DC to 60 Hz is ± 2.5% at best (± 1.5% + 10 counts) and degrades to an unacceptable ± 10% + 20 counts between 1 MHz to 25 MHz. Worse yet, for a 200 MHz analog Bandwidth Unit, the accuracy isn’t even specified for an RMS or TrueRMS reading above 25 MHz, but the manual says it will degrade as the instruments frequency rolls off.
The unit is designed relatively ergonomically as its size is 10.5” x 7.5” x 2.8” and weighs a mere 4.8 pounds including the battery. It has four each, color-coded BNC inputs at the top and out of the user’s way. It also has a side handle for carrying it and a removable top strap for hanging the unit which is not only convenient, but also is a safety feature as it allows the user to keep hands off as much as possible. This is very handy when working on high voltage circuits. Another feature is the probes themselves (four included with the unit). They are color-coded to match the BNC input colors, which in turn, match the trace colors. The probes are all 300 Mhz with 10:1 attenuation. Therefore, they should not affect accuracy much even at the full 200 MHz analog limit of the unit. The display is not as big as I’d like, but it’s adequate for most work and when it’s not, the waveforms can be downloaded and the user can do post-processing using Excel, Matlab, MathCAD, Mathematica, or other math software on a PC with a large screen.
One of the best things I like about this scope the dynamic range, which is 100uV using a 1:1 (direct) probe or 1mV using a 10:1 probe and being battery operated, it won’t be affected by capacitance from the 120 VAC Input of the power supply to the digitizers. The maximum range is also excellent at 300 V with a 1:1 (direct) probe or 1,000 V using the 10:1 probes. Not many scopes can brag about a dynamic input range like that. The CMRR at DC is greater than 100 dB and for AC, greater than 60 dB at 50, 60, or 400 Hz.
Another very useful and rarely seen feature that I made use of while testing an Inverter design of mine is that all four channels are isolated from each other, but only up to 30 V. In my case, this was enough for battery-operated inverters. It let me look at my drive signals from my DSP chip and at the same time, the isolated gate-drive to my power FETs and the output of my power FETs. I had to buy an expensive Isolator unit to use with my LeCroy lab scope that was only two-channel to get the same effect. Of course, the lab scope isolator unit could withstand much higher ground differentials than 30 volts. Still, this is a great and very useful feature. However, one must be careful that all channels of the isolated signals, especially if fast switching, have the probe return (ground) side going to the ground end or else the capacitance between channels can distort the signals.
I’ve included a few photos that show the unit and it’s case and power supply. I would definitely recommend this scope for those that need a relatively high-end portable scope capable of running on batteries, otherwise, the newer lab scopes, like the LeCroy Waverunner series that have similar bandwidth and are not that much bigger are a much better bet for general use, but they don’t run on batteries and they are much more expensive.
Kamran Kazem, V.P., CTO
Magnetic Design Labs, Inc.
