EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: calzap on March 09, 2015, 04:58:56 am
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I bought a GW Instek GDM-461 multimeter because I wanted to record voltages for battery discharge tests. It looked like a decent handheld multimeter (22000 counts vs 10000 for my Agilent U1241AN). My main bench DMM is the Agilent; I use a less expensive Extech 310 in the field (it gets dropped and misconnected a lot). I have some other Instek gear that has performed well. The price was right (about US$100), and it has serial output and included software. I unboxed it, looked through the manual, and started using it.
The supplied battery is a no-name carbon zinc. At least it's a 9 V; so leakage isn't likely to occur. Screws retaining the battery case and instrument back are coarsely threaded self-tappers. It has no light for the display, which is odd, considering it's the top of the handheld line, and some of the lesser models do have a light. It doesn't have the auto power-off that some of the lesser models have. It has a very solid feel in the twist and bend test and a nice rubber-bumper periphery.
The specs for accuracy are similar to the Agilent for most of types of measurements, but it has more resolution. The input impedance is 10 Mohms except in the mV range it's 3 Gohms. It has no capability for measuring temperature. As a frequency counter, the specs say it can go to a phenomenal 220 MHz (not true, see below). It has autoranging, but ranges can be selected manually too. The continuity beeper is very quick and adequately loud.
The supplied probes are similar to the large Agilent probes in look, feel and size. I'm not likely to use them much because I prefer Parrot probes for routine work and Agilent microprobes for tight spaces. It also comes with a funky little adapter called a multipurpose socket. The adapter plugs into the meter and has sockets and test pads for connecting various components (resistors, diodes, transistors, etc.) for testing. I haven't used it. The digits in the display are a little larger than the Agilent, and the display has more contrast than the Agilent. The knob has a nice feel and the lettering around it is more easily read than for the Agilent. Most of the controls are fairly intuitive to decipher and use.
I tested it with my DMMCheck, and voltage (5 V), resistance (100, 10 & 1 K) and current (1 mA) were all in spec. Tested the frequency counter with a GW Instek GFG-8250A function generator up to 5 MHz, and it was spot-on for square and sine waves. Above 5 MHz, I used a Signal Forge SF800 with a square wave of +/- 3.3 V. It was spot-on up to 30 MHz and completely failed a little above that. Did not really check capacitance measurement except did connect a 1.50 uF poly cap, and it gave the same reading as the Agilent.
There are a couple of pics of the unit below. One is a front view; the other is with the back off. To my inexpert eyes, the jacks don't look that well designed. They are one-piece split barrels with a slim tabs that run from the bottom of the barrels to the main board where they are soldered. In the Agilent, the metal barrels are in independent plastic cans, and their bottoms are soldered to a daughter board. The input protection looks pretty good though. HCR fuses, a board gap and a bunch of PTCs and ZOVs. The only compliance mark is a CE. If I did want to check mains voltage on the utility side of the service entrance breakers, I'd use the Agilent. It has more compliance marks, and I trust the brand more.
Data is transmitted optically to the included serial cable with an IR LED. The IC near the LED is just a hex inverter. And no, I didn't take the board out of the case, so the front side will be a mystery for now.
I installed the software and connected the meter to my PC. The opening screen showed COM1, but my computer was using COM5. Looked for a tab or button to change COM ports. After some experimenting, found that a click on COM1 changes it to COM2; click again, it goes to COM3. Tops-out at COM4, so no COM5 or higher. Went to Device Manager in Windows and found that COM1 and COM2 were un-used. Right-clicked on COM5 (happens to be a FTDI USB cable) and changed it to COM1. Then everything worked smoothly. Apparently the meter uses 9600 bps because that was where the COM port was set in the device manager.
The manual for the software is nearly useless, so it took a bit more experimenting to figure out the various controls and functions. But I was able to control the rate of data collection and save it to a file. The program has an option to save in Excel format, but it actually saves it as a txt file with an xls extension. Better to save it as a txt file and then import it into Excel or some other program. Data is space-delimited in the txt file.
So far, I'm happy with the unit; it's doing what I bought it for. Will it replace the Agilent as my main bench meter? Nope, except where its range and resolution exceeds that of the Agilent and I need the extended range or resolution. It'll be used as a backup and for data logging. Would I recommend it as a main handheld DMM for others? If you can afford a Gossen, Fluke or Agilent (now Keysight) with similar capabilities, that should be your choice. In its price and capability range, it should be considered. You're not likely to find one of this quality for data logging for less money.
Mike in California
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It is nice to see the insides of this variant. You need to know that this is the Uni-T UT61E rebadged. It is not just a rebadge though as this actually seems to have proper input protection. It is still labeled for 250V only on the current ranges? The manual shows it needs 1000V fuses as does your image of the insides.
A UT61E sells for around $50 to $60 usually. This cost how much? I can only find it for $140 or so.
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It was US$100 from tequipment.com. Not sure of the maximum V for current measurement. For mains range of voltages, I use clamp-on or purpose-designed plug-in ammeters.
Mike in California
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It is printed by the current probe jacks what the voltage is. On the GW Instek site the product image shows 250V max. This would be incorrect according to the manual and the fuses installed. AT $100, it is a good buy IMHO with the proper input protection over the UT61E.
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Nice review, thanks.
I was curious if you had a chance to test the RS232 output and determine what sample/output data rate the unit supports.