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Author Topic: Got to be woth £20 uk  (Read 50891 times)

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Offline Anks

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Re: Got to be woth £20 uk
« Reply #1 on: June 11, 2013, 05:50:34 AM »
"High Precision" and china don't normally go together but you never know.
 

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Re: Got to be woth £20 uk
« Reply #2 on: June 11, 2013, 05:55:11 AM »
"High Precision" and china don't normally go together but you never know.
I know but for £20:00p curiosity is getting the better of me, it would be nice if it was a gem though. Dave should get one and tear it down :-+
 

Online mikeselectricstuff

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Re: Got to be woth £20 uk
« Reply #3 on: June 11, 2013, 06:14:44 AM »
For the amount of times you'd use something like this, the rechargeable battery is probably a bit OTT.
And the 5V power in is NOT a USB connector - WTF?
And how much accuracy do they lose with that switching system I wonder?

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Offline madires

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Re: Got to be woth £20 uk
« Reply #4 on: June 11, 2013, 06:16:13 AM »
The question is if it's a genuine AD584LH. Just saw Chinese offers for US$4 and a more reliable one asks for US$35. 
 

Online Galaxyrise

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Re: Got to be woth £20 uk
« Reply #5 on: June 11, 2013, 06:36:53 AM »
The PentaRef from voltagestandard.com is only a little more, and probably worth it given the calibration, TLC, and good reputation (not to mention 5 user-selectable voltages.)
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Offline npelov

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Re: Got to be woth £20 uk
« Reply #6 on: June 11, 2013, 07:07:00 AM »
@Galaxyrise I would also suggest that.
It also can help you trim any adjustable reference like TL431 to <0.1% by measuring difference between the two with simple inexpensive voltmeter in mV range.
 

Offline amyk

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Re: Got to be woth £20 uk
« Reply #7 on: June 11, 2013, 08:12:15 PM »
The question is if it's a genuine AD584LH. Just saw Chinese offers for US$4 and a more reliable one asks for US$35.
Does one even exist? I see no mention of an LH variant in the AD584 datasheet on Analog's site. The variants there range from $3.17 to $33.90 in 1ku so those prices don't look that far off.
 

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Offline madires

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Re: Got to be woth £20 uk
« Reply #9 on: June 11, 2013, 10:27:03 PM »
The question is if it's a genuine AD584LH. Just saw Chinese offers for US$4 and a more reliable one asks for US$35.
Does one even exist? I see no mention of an LH variant in the AD584 datasheet on Analog's site. The variants there range from $3.17 to $33.90 in 1ku so those prices don't look that far off.

It's not in the Rev C datasheet but in the older Rev A. The differences are:

OUTPUT VOLTAGE TOLERANCE
Maximum Error1 for Nominal
Outputs of:
10.000 V   +/- 5mV
7.500 V     +/- 4mV
5.000 V     +/- 3mV
2.500 V     +/- 2.5mV

OUTPUT VOLTAGE CHANGE
Maximum Deviation from +25°C
Value, TMIN to TMAX2
10.000 V, 7.500 V, 5.000 V Outputs      5 ppm/°C
2.500 V Output                                    10 ppm/°C

But I guess that the AD584LH isn't produced anymore.
 

Offline iloveelectronics

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Re: Got to be woth £20 uk
« Reply #10 on: June 15, 2013, 02:09:19 AM »
Martin just had a quick look at this device:

Jump to around 22:04 to see his first look review.
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Offline madires

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Re: Got to be woth £20 uk
« Reply #11 on: June 15, 2013, 04:55:02 AM »
Martin just had a quick look at this device.
Jump to around 22:04 to see his first look review.

Looks to be genuine. It amazes me that the producer can source the AD584LH for such a low price that he is able to sell the finished product for 20 bucks.
 

Online Fraser

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Re: Got to be woth £20 uk
« Reply #12 on: June 15, 2013, 05:40:13 AM »
GBP20 is the average cost of an evening in the pub so I just stayed in this evening and ordered one  :-+
 

Offline [email protected]

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Re: Got to be woth £20 uk
« Reply #13 on: June 15, 2013, 06:14:11 AM »
GBP20 is the average cost of an evening in the pub so I just stayed in this evening and ordered one  :-+

Are you shure you ordered one with the "calibration certificate"? The ones I found on eBay and Aliexpress all didn't mention it, and only listed the PCB or PCB plus enclosure as the shipping contents.
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Online Fraser

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Re: Got to be woth £20 uk
« Reply #14 on: June 15, 2013, 06:27:04 AM »
No mention of certificate but I can check it against a recently calibrated lab meter so can produce my own calibration table  :)
 

Offline KJDS

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Re: Got to be woth £20 uk
« Reply #15 on: June 15, 2013, 06:52:30 AM »
GBP20 is the average cost of an evening in the pub so I just stayed in this evening and ordered one  :-+

I've regularly had rounds that cost three times more than that. I probably need slightly less drunkardly friends.

Online Fraser

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Re: Got to be woth £20 uk
« Reply #16 on: June 15, 2013, 08:20:19 AM »
 ;D
 

Offline 807

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Re: Got to be woth £20 uk
« Reply #17 on: June 15, 2013, 08:10:06 PM »
Even cheaper if you buy in US$.

Got mine for $24.69 = £16.23 at current PayPal rates.

http://www.ebay.co.uk/itm/400452242651?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

No mention of a certificate on any of the Ebay listings though.
 

Offline staxquad

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Re: Got to be woth £20 uk
« Reply #18 on: June 16, 2013, 01:08:00 AM »
Even cheaper if you buy in US$.

Got mine for $24.69 = £16.23 at current PayPal rates.

http://www.ebay.co.uk/itm/400452242651?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

No mention of a certificate on any of the Ebay listings though.

even cheaper without the box @  US $15.99 (sold last month, don't know if more will be offered)

http://www.ebay.com/itm/New-AD584LH-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-/221210908532?pt=LH_DefaultDomain_0&hash=item3381329774




They are a bargain with the calibration certificate, giving 6 usable digits, but without the calibration certificate , you could only use 4 digits.  If you're looking for a unit to verify calibration, without the calibration certificate, you're a little short in accuracy to even check a 20,000 count Fluke 87.  With calibration certificate, or if you have access to a calibrated device to give it 6 digits of accuracy, it's good for a 300,000 to 500,000 count meter.  MJLorton's test was impressive with calibration certificate.

I considered what was on offer from a PentaRef ($61) to decade references and decided to watch out for decade references on Ebay as a better value for more versatility.  Came across a 7 digit Kelvin Varley Divider (DAS57AL, $99.99), 0 to 1 volt DC and 0 to 10 volt DC, shown at auction dialed to 7.777700VDC and tested by an HP 34401A to 7.7776VDC, so I went for it.   

Testing after receipt revealed that set to 10.00000VDC, both my HP 3478A units showed 10.0000VDC with no flickering, steady the whole day (still at 10.0000VDC 2 days later, never turned off, did drop down to 9.99999VDC or 9.99998VDC when the temperature plummeted 1 or 2 degrees).  My Fluke 87III showed 9.995VDC.  Even my old Philips nixie showed 9.95VDC.  Will be trying to verify the DAS57AL to it's full 7 digits, but presently, I think I have confidence in it's ability to verify the HP 3478A's 300,000 count. 


« Last Edit: June 16, 2013, 03:09:46 AM by staxquad »
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Offline iloveelectronics

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Re: Got to be woth £20 uk
« Reply #19 on: June 19, 2013, 12:52:40 PM »
I just got myself one of these. Measurements taken with my used HP3457A with unknown calibration history (numbers in brackets are the valued marked on the sheet that comes with the voltage ref):

2.49841 (2.49840)
5.0007 (5.00090)
7.4977 (7.49807)
9.9996 (10.00007)

No complains here for the little money I paid :)
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Offline Stonent

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Re: Got to be woth £20 uk
« Reply #20 on: June 19, 2013, 02:16:08 PM »
Appears to be powered by a Samsung GT-i9000 battery
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Offline poorchava

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Re: Got to be woth £20 uk
« Reply #21 on: June 19, 2013, 03:51:44 PM »
What are they using to switch the voltage with the button? Analog mux? mosfets? Seems like most of those methods are no good for high precision measurements...
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Offline Stonent

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Re: Got to be woth £20 uk
« Reply #22 on: June 19, 2013, 06:17:02 PM »
I see 4 P-FETs and a JFET OpAmp, that's what I could get from part searches, also a charging chip in the top corner.

The ebay description also says

Quote
The MCU switch 4-way reference voltage output with LED indicators

So some kind of Microcontroller?  That T1 chip looks suspicious. Pin 8 appears to be grounded, it could be a PIC12 series?
« Last Edit: June 19, 2013, 06:30:09 PM by Stonent »
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Offline madires

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Re: Got to be woth £20 uk
« Reply #23 on: June 19, 2013, 10:55:29 PM »
I see 4 P-FETs and a JFET OpAmp, that's what I could get from part searches, also a charging chip in the top corner.

The ebay description also says

Quote
The MCU switch 4-way reference voltage output with LED indicators

So some kind of Microcontroller?  That T1 chip looks suspicious. Pin 8 appears to be grounded, it could be a PIC12 series?

There are two ways do set the output voltage of the AD584. One is to connect the output pins as described in the datasheet. And the other one is to connect a voltage follower to one of the outputs or each output (you can have all 4 output voltages at the same time).

Based on the 4 p-ch FETs and the single OpAmp I'd guess they switch the selected output of the AD584 to the OpAmp acting as a buffer.
 

Online Fraser

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Re: Got to be woth £20 uk
« Reply #24 on: June 27, 2013, 10:16:51 PM »
My voltage reference unit arrived today from this seller:

http://www.ebay.co.uk/itm/400452242651?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

GBP16.10

Ordered from Hong Kong on 22 June, arrived with me in the UK 27 June.... pretty good service  :)


My comment on it....

SUPERB !  :-+

It arrived wrapped in a soft 'silk' cloth to prevent scratches. It was then wrapped in 2 layers of bubble wrap before being paced in a padded envelope.

It includes the all important calibration certificate. I checked the output on my Fluke  87 III using its 4.5 digit mode. All readings tallied with the calibration certificate within the capabilities of 4.5 digits. I will test the unit on a calibrated lab multi-meter tomorrow.

For the money I consider this a bargain purchase. I definitely recommend buying the cased unit as the case protects the PCB and is very well made.

I can check its calibration any time I want with the office calibrated unit so I will effectively have a calibrated transfer standard.  :-DMM Whoopee !

I purchased some close tolerance resistors last year so now I just need a current standard....time to look at the specs for this unit to see if it can drive a resistor load and what current it can produce  ;) Otherwise I will use it as a voltage reference to build a simple current reference add-on. GBP16 well spent.

Picture attached

I have another in transit from China (this one came from HK) I will be ordering another from the HK supplier and it will be interesting to see how the three units age over the coming year. At GBP16 these really are worth having lying around the lab for a quick meter accuracy check.
« Last Edit: June 27, 2013, 10:44:42 PM by Aurora »
 


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