Panel meter, analog VS digital

[Johnson777717]

Heya folks! I need some assistance again, if I may?

Is it possible to create an accurate micro-ohm meter with a common digital panel meter?

I'm working on an ESR circuit that calls for an analog 100 micro ohm meter which in turn outputs "resistance" within a 0.1Ohm tolerance ( I think, anyway, the tolerance is pretty tight).

I've been using a digital panel meter PM128E for most of my projects that involve some sort of display (voltmeter, ammeter etc). The PM128 is setup to read a 200mA scale, but I don't know what the tolerance is for this particular meter. I'm thinking theoretically, I can break the scale down to 200uA with a voltage divider, but the question of accuracy arises.

What do you folks think? Should I just stick with the analog meter? I'm not really looking to go with a tight tolerance panel meter, because of the cost concerns. I just can't justify a $40 panel meter for a simple ESR meter, when an analog meter is available for $10 or so. Although, if I can get good accuracy with a regular panel meter which costs $12, then so be it. Oops, I just found out that the panel meter is +-0.5% accuracy at full scale. So I may have answered my own question. Still....

Any advice? Thank you for your time.

Panel meter example.
**broken link removed**

 

[Dean Huster]

Micro-ohms? Even with milliohms, or less than 10 ohms, the only way that you're going to get an accurate measurement is with a Kelvin or 4-terminal measurement technique so that you eliminate all test lead and contact resistance from the measurement. I can't imagine need to measure micro-ohms anyway.

Dean

 

[Klaus]

Also, with all digital meters you have to consider an accuracy of +- 1 of the least significant digit, since the meter cannot show half digits .

For your micro Ohm meter you need a 4 wire sensor, two to pass a rather largeish current through the connection under test and the other two to your meter (amplified?), to sense the voltage difference.
Klaus

 

[Johnson777717]

I'm sorry folks. I made a mistake in my previous posting. When I said Micro-ohm meter, I meant Micro ammeter. Ooops.

 

[Russlk]

This may be a bit off topic, but one advantage of an analog meter is that there is only one needle to observe, so you get an instant idea of what is happening. The digital meter shows 3 or more numbers which you have to interpret in order to know what is happening, so it takes longer.

 

[Johnson777717]

Very good point RusslK, which is one of my delights in an analog meter.

For this application, I'm leaning toward the analog meter, simply because of the cost associated with developing an accurate digital meter, and as RusslK stated, the analog version simplifies both the circuit as well as the interface.

Thanks for your input folks! I appreciate it.

 

[Dean Huster]

I'm an old analog man myself, but it takes a lot of electronics to make an analog meter as accurate as a digital meter (e.g., the differential voltmeter). But you can't beat an analog movement for enhancing your ability to peak or null an adjustment. That's why those digital THD distortion analyzers absolutely must have automatic nulling circuitry, because it would take you forever to null by hand against a digital movement.

However, I've noticed that analog movements are getting really pricey these days, and if you don't need the analog advantages, the digital panel meter may be more cost-effective if you have to buy new vs. working from a "junkbox".

Dean

 

[Johnson777717]

I agree Dean. Luckily, the circuit is analog so I won't be running into a digital zeroing situation.

Unfortunately, I don't have an analog meter in my junkbox collection, so I'm on the market, so to speak.

Your point about the analog prices rising seems true to me as well. Digikey wont sell an analog meter for less than $20 or so. Most are $30-$40!!! This is also similar to Mouser, local stores and some other electronics retailers. Lucky, I've found a uA meter for about $12 at allelectronics.com, so I think I may become a patron. Of course, a digital meter is also around $12, so this is where I have become torn between the two.