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ko4nrbs

Mini Dc Volt And Amp Meter Selections Updated Reply 2/5!

2 posts in this topic

I've been comparing the small Mini volt and amp meters available on Ebay, etc. One thing that jumped out at me was the specifications must be checked in order to get the accuracy you want. The meters do not all have the same specifications so beware before purchasing.

 

From HKJ:

First you have to look at the number of connection wires on voltmeters:

2 wires means that it draws power and measures on the same wires.

3 wires means that it has a separate power connection, this usual allow the meter to measure down to zero volt (Power input must, of course, not be zero).

3 wire vs. 2 wire- Is the 3 wire more accurate?? From HKJ on the 2 wire -The voltage drop due to the meter's power consumption will often be negligible, but if you want to measure current also, it can be significant.

 

Refresh rate is how fast the display updates, for just checking voltage it does not matter, but if you have to adjust voltage you want at least 3 times second, preferably is 5-6 times a second.

 

Accuracy and resolution only depends on what you need, a typical cheaper multimeter is about 0.5%

Input impedance is only interesting if you measure in sensitive circuits, not when checking a battery.

Meters_zpsop5kajox.jpg

 

Here is an example of meter specifications I found:

Working current:≤20mA

Display:0.28" color red

Voltage resolution (V): 0.1V

Current resolution (A): 0.01A

Measure accuracy: 1% (± 1 digit) (I've seen some down to .1%)

Measuring range: 0V-30V

Minimum resolution (V): 0.1V

Refresh rate: ≥100mS / times

Volt Meter example for .1% Accuracy:

3 Wire

https://www.adafruit.com/products/705

2 Wire

https://www.adafruit.com/products/460

 

An amp meter example with accuracy: about 0.02A:

amp%20meter_zps4tgvvp55.jpg

http://www.ebay.com/itm/0-36-DC-Amp-Ammete...%3D162276757613

 

 

 

Personally, I'm going to compare meters looking for the best Resolution, Refresh Rate, Input Impedance and Measurement accuracy. In addition for best accuracy don't use a 100 volt meter to measure low voltages, i.e. 5, etc.) It's best if the meter reads midscale for best accuracy, i.e. 0-100 volt meter reads midscale for 50 volts.

 

 

Don't assume the meter you are using is accurate until you test it against a know accurate Multimeter, etc.!!

Bill

Edited by ko4nrbs

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Just got this as a reply to one of my questions:

For accuracy such as you would find in a handheld DVM, I like the panel meters that you will find with a higher resolution of accuracy such as the 3 1/2 digit or 4 1/2 digit. A 3 1/2 digit meter has a max reading of 1999 and a 4 1/2 digit has a max reading of 19999. That is not volts but just the max reading on the display. Where you put the decimal point is optional based on which display you buy. The 1/2 signifies the "1" in the display. You can buy these in 200mV, 2V, or 20V max input. Any higher voltage would require a voltage divider and then you set the decimal point on the display as necessary.

 

Therefore a 0 to 5Vdc range would require a 20V display if you did not want to mess with voltage divider resistors. Thus a 3 1/2 digit display would require setting the decimal point such that you would get 2 decimal place accuracy with a max reading of 19.99 or 19.999 on a 4 1/2 digit display. These types of meters are more expensive.

 

The cheaper types utilize the on-board analog to digital converter in a microcontroller where the accuracy is a function of the number of bits of the A/D converter. They are cheap because you just need a microcontroller, some 7-segment LED digits and the firmware, which after it has been developed costs nothing. But they won't be as accurate as the analog chips that provide the LCD drive to a 3 1/2 digit or 4 1/2 digit LCD. You will notice that all digital voltmeters use 3 1/2 or 4 1/2 digit displays.

 

Search on Ebay for "3 1/2 digit panel meter 20v". Price looked fairly reasonable. The cheaper and less accurate meters will not bother with a "1" on the far left side of the display.........nor do they fall into a category of 200mV, 2V, or 20V. There are some current meters too.

 

Bill

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