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Re: Optimal full scale deflection on analog meters: What would HP DO??


Rodger Bean
 

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AVO¡¯s 1, 2.5, 10 ranges look less cluttered to me (but then I am used to my AVO 8 Mk2 that I bought in 1965). The 1, 3, 10 sequence gives a visual ¡°beat¡± between the tick marks on the two scales. Going for an E-04 or higher sequence would make the scale even more cluttered.

Another sequence was used by Sangamo Weston on the S68 series of dynamometers (voltmeter, ammeter and power), which was 10, 20 & 50 on the voltmeter. The scale on these is very cramped at the low end, the first two tick marks are 0 and 2. The distance between the 2 & 3 is approximately 12.5mm and between 9 & 10, 50mm.

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One aspect of the moving coil meter is that it averages fluctuations that are faster than the needle¡¯s response. Also, the inertia of the movement means that it acts as a low pass filter. I find trying to do a null adjustment with a digital display frustrating. In addition, a DMM used on the bench for nulling can suffer from its high input impedance, which makes it susceptible to stray pickup. I live within 5Km of six, high power AM stations (ERPs of 5 - 20KW).

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Regards

Rodger Bean

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From: [email protected] <[email protected]> On Behalf Of Dr. David Kirkby, Kirkby Microwave Ltd
Sent: Monday, 22 August 2022 06:25
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] Optimal full scale deflection on analog meters: What would HP DO??

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On Sun, Aug 21, 2022 at 12:10 PM, magnustoelle wrote:

Or Rohde & Schwarz, may I add ?

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Cheers,?

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Magnus?

Although the scales are marked 3.0 and 10 on the R&S instrument, I note that the full-scale on the 3 V range is 3.2 V. It looks to me as if the 10 aligns with sqrt(10)=3.16. I think if you assume your inputs are randomly distributed, you can't beat that if there is only one other scale between 1 and 10.

To keep a reading at least 50% of full scale, I think one wants FSDs of
1, 1.77828, 3.16228, 5.62341 and 10.

Perhaps calling them 1, 2, 3, 5 and 10 would not be too bad. Just ensure the 3 V scale can actually read up to 3.1622 and the 5 V scale up to 5.62341

I like the idea someone had earlier of offsetting the scale, so the left does not read zero. That would actually be quite neat for my application (Q-meter), because one wants to peak up on something carefully. I will probably drive the meter from a DAC, because I can use a computer to flatten the frequency response, so it does not matter if the output power of the oscillator, or sensitivity of the detector changes with frequency.

I don't know if there's any real advantage in moving coil meter, compared to a decent analogue scale on a digital display. I don't mean a bar-graph with 10 segments, but implement something where there's at least 400 pixels across.

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