Analogue 19" Rack Power Meter - Page 1
Forum section: electronics / projects

author: XL5
author_rank: Contributor
timestamp: June 13, 2014, 08:47:22 am
content: I want to build a power meter for myserver rack. I am going to usethis ammeterandthis voltmeter, which I got for £9.99 each off eBay.They look like they should be DC, but the seller has told me they are AC Meters, this will be a bit of a non-starter if they are not.My question is, how should I wire these? My plan was to simply put the voltmeter in parallel and the ammeter in series on live. Will this work? or cause a horrible fire?

author: Thilo78
author_rank: Regular Contributor
timestamp: June 13, 2014, 08:59:29 am
content: As from the markings on the front, I'd guess that they are suitable for AC and DC.Also, the voltmeter should be able to be wired to your 230V supply directly, whereas you have to check the ammeter:Panel meters for AC use are often designed for use with current transformers. The ones I have are rated for 1A (today's standard) or 5A (earlier, more or less obsolete) secondary current.If you can't find documentation, you should check that by applying a known/measured current through the terminals.Keep that current below 1A to start with, so that you can check polarity (for DC) and see what the ratio is.

author: XL5
author_rank: Contributor
timestamp: June 13, 2014, 09:02:05 am
content: Awesome, thanks for your help. Hopefully these will arrive today so I will get onto testing these this weekend.

author: Thilo78
author_rank: Regular Contributor
timestamp: June 13, 2014, 09:29:58 am
content: Look at the front of the panel:You see a horizontal line there with a sine symbol below. With the meters I know this means that they are suitable for AC and DC measurements. (at least according to German VDE markings)edit: Definitions are in DIN 43 802 and VDE 0410. I think there are equivalent IEC standards available for this)The star with the "2" in it means it has originally been insulation-tested up to 2000 V. I wouldn't bet on that with the given age"2.5" means a total accuracy of 2.5% relative to the max value of the range (15 A).As for the measurement principle itself, it's marked as moving iron arrangement. (it's the little coil symbol with the line in it)So I'd expect it to even give you true RMS values.Interestingly enough that the mounting position is not marked. I'd think it's intended to be used in a vertical panel.If mounted horizontally, it might have wrong readings...If you receive the meters, please post some pictures of the stickers on the side of the case.Maybe I can tell you more based on that information.Thilo

author: XL5
author_rank: Contributor
timestamp: June 13, 2014, 09:35:13 am
content: I will post pictures as soon as they arrive (And as the project progresses).I thought that the sine/line symbol meant that they will be capable of AC measurement, good to hear that's likely correct.They will be going in the front of a rackmount box so will be mounted vertically.

author: XL5
author_rank: Contributor
timestamp: June 13, 2014, 02:59:47 pm
content: Boo, looks like I'll be waiting until Monday for the parts to arrive...

author: Fank1
author_rank: Regular Contributor
timestamp: June 13, 2014, 09:35:25 pm
content: AC only the dead give away is the non linear scaling.They are "vane" type meters.

author: XL5
author_rank: Contributor
timestamp: June 16, 2014, 10:44:47 pm
content: The meters and the rack enclosure arrived today. The voltmeter works as expected, measures AC voltage perfectly.The Ammeter, I have a number of problems with. Firstly, the meter only reads 0 when the dial is facing up. When the meter is positioned with the face vertical, the needle points to about 7 amps.The second issue is likely user-error. I can't seem to make the meter do anything interesting, I tried hooking up in series with a laptop power supply and it didn't react at all to power being drawn.What should I do to work out how to drive the ammeter, or has it been damaged in shipping?The only further information on the front is "No D.9414" and "1978/6" which is presumably a model number and manufacturing date. The sticker on the side is just a warranty seal.To end on a positive note, the meters look freaking awesome with an LED in the bottom.

author: richard.cs
author_rank: Super Contributor
timestamp: June 17, 2014, 08:53:54 am
content: Quote from: XL5 on June 16, 2014, 10:44:47 pmThis is pretty normal, they are designed to work in a specific orientation. Try adjusting the zero by turning the little screw in the centre. This may have the desired effect but sometimes they really do only work one way up.Quote from: XL5 on June 16, 2014, 10:44:47 pmIt should work on both AC and DC but note the compressed scale at the low end. A 2-3A laptop supply (and less current is actually drawn unless the battery is flat) is barely going to make it move. Try some more current, perhaps a couple of headlamp bulbs and a car battery.

author: The Electrician
author_rank: Frequent Contributor
timestamp: June 17, 2014, 09:40:42 am
content: Using separate ammeter and voltmeter measures volt-amperes, not watts. If your equipment has a poor power factor, the error could be substantial. Why don't you get a actual wattmeter? Look here:http://www.ebay.co.uk/sch/i.html?_sacat=0&_from=R40&_nkw=wattmeter&_pgn=2&_skc=50&rt=ncSomething like this would be good:http://www.ebay.co.uk/itm/DIGITAL-WATTMETER-ENERGY-METER-DIN-RAIL-MOUNT-kW-AC-ZD1-/360962155027?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item540b056213Or a mechanical one:http://www.ebay.com/itm/Vintage-Simpson-Model-390-Volt-amp-wattmeter-/181436085388?pt=LH_DefaultDomain_0&hash=item2a3e6ef48cWhat's your expected maximum power? This goes up to 1500 watts:http://www.ebay.com/itm/WATTMETER-SIMPSON-0-TO-1500-300-VOLT-10-AMP-New-In-Box-/321368474784?pt=LH_DefaultDomain_0&hash=item4ad30dc4a0

author: XL5
author_rank: Contributor
timestamp: June 17, 2014, 09:43:12 am
content: The UPS and PDU in the rack already record that information (And it is saved to an SQL database and accessed through a web-app. )This is just a cool visualisation of roughly what's going on.Quote from: richard.cs on June 17, 2014, 08:53:54 amThe adjustment screw in the front changes the value a bit, but not much. I guess this is a horizontal meter. That's a pain, is there any way to change that?

author: XL5
author_rank: Contributor
timestamp: June 19, 2014, 12:34:11 pm
content: Quick update, and it's good news!The seller has sent a replacement ammeter, and this one looks in much better shape, and reads 0 when held vertically. When I get home from work today I will test it out.

author: XL5
author_rank: Contributor
timestamp: July 07, 2014, 10:13:04 pm
content: I'm back from my holiday, and I've been trying to get this ammeter to do anything interesting.I have wired it in series, with a computer drawing about 1A and nothing much happens. Am I just not putting enough through it, or is it something else?I'm wary of pumping 5-6 amps through it before I know it's a 1:1 scale because I don't want to blow it.

author: Thilo78
author_rank: Regular Contributor
timestamp: July 13, 2014, 11:48:51 am
content: I dare say, that if it doesn't show much with 1A, then it's likely to be a direct 15 A ammeter.Do you have a bench PSU, that you could use to ramp up the current?Then you would see something happening, and shut off quickly, if you feel something's going wrong.If it was rated 1A, it should have had a full scale reading; with 5 A rating, it should be somewhere around 1/4th of the scale.