Autoranging Panel Meter

[MrAl]

Hello,

Has anyone run across any autoranging panel meter? They have the standard type but cant seem to find autoranging type for a reasonable price like 20 dollars or less.

Thanks...

[sghioto]

Geez MrAl what do you expect for only twenty bucks?
For $22.00 you can purchase an entire meter (like the one in the link below) and just hardwire the function needed, unless space is an issue.

http://www.provantage.com/steren-electr ... TEN0FC.htm

Steve G.

[Robert Reed]

I'm curious. Usually a panel meter is a dedicated device to monitor a piece of equipment's functions within its normal range. What is your application for?

[MrAl]

Hi again,

I greatly appreciate both of your inputs on this.


Steve:
Yes i know about small multimeters, but you have to realize that they are not made to run like a panel meter is. The difference is a multimeter requires a battery whereas a panel meter takes a power supply input instead of the battery. The difference there is that you can not connect a power supply to the multimeter and expect to be able to measure that same power supply or anything else connected directly to its ground. The panel meter is made for this purpose, and has a voltage input as well as a measurement input.
BTW even some panel meters wont work without a separate isolated dc power supply.

Robert:
The application is for an adjustable bench switching power supply. The problem with this unit is the meter that is on there only reads three digits, and those three digits have a fixed decimal point. That means it reads "30.0" for 30 volts, but when you turn it down to say 2 volts it reads "02.0", which looses one digit already. When you turn it down to 0.1 volt, it reads "00.1" which is ridiculous.
I need it to read "1.03" for example or maybe even "0.13" but better yet "0.135" for example.
The power supply is ok i guess, but the meters that came with it bite.

Oh yeah, it would be nice if the meter lights up too like an LED meter or backlit LCD.
Of course i could build my own meter with a uC chip, but i dont want to have to take the time to do that.

[Robert Reed]

Oh OK, A piece of bench test equipment, now it makes more sense to me. One thing you might consider for 'quick and dirty' is a range switch providing the internals are readily accessible. Most of those meters start out with a 200 mv full scale sensitivity. I know it can be a pain in the a**, but not too bad if your work dwells on just one range for an extended period of time.Its one way to get the resolution your looking for although adjusting your voltage out put to that kind of resolution at low levels may be touchy.
Is this the Mastec Supply you had posted about a few months ago?

[sofaspud]

Someone may sell an autoranging module, but I can't recall seeing any. You could go the DMM route with an isolation circuit; eg the
ICL7660 or switched capacitor apps that can be found online. As another idea to go along with, you could wire the meter to provide
an output current measurement, too, with a turn of a switch.
And as I'm sure you know, a DMM can be had for less than any panel meter. Another one of life's quirks.

[MrAl]

Hello again,



Robert:
Oh yes, that may be an option. Normally if i tune down low i will be reading that low for quite a while i think. I guess a set of ranges like 200.0, 20.00, and 2.000 would probably do it, maybe with 0.2000 if that was possible. That would mean a four position switch. Maybe a slide switch would do it as front panel space is going to be limted after i add a secondary (and possibly third) internal power supply to this thing. That will require two knobs and two binding posts, and that uses up all the front panel space except for where the meter will actually show through.
I wouldnt mind designing a circuit to autorange i guess, but gee i was hoping to buy one and stick it in there rather than have to construct one.
This is the Mastec i was asking about the schematic for, which BTW i got finally. The other Mastec months ago was the 50000 count blue fluorescent display meter, which seems to work ok i guess without mod. Just this bench supply has panel meters that dont autorange so it's difficult to see down low like around 1.00 volts or 1.00 amps or even 100ma... ie 100ma shows up as "00.1" amps, which is almost useless.
There's lots of room inside this case though because they use the same case for a model that is rated 3 times higher in current output. That means there is quite a bit of room for added stuff, except the front panel is already quite filled up with stuff, unless i remove one of the meters already there...hmmm, might work.

sofaspud:
Yes i can not recall seeing any either. If i use a DMM i would have to light it up myself and also use a dc to dc swithing supply to power it. It's doable i guess, but more work I'd also have to find a small one that autoranges that will fit inside the case. Did you see any real cheap autoranging dmm's around?

[Janitor Tzap]

This only has to read voltage only?

If that is the case.
I was over at Walmart in their auto/boat section.
I found a 4 digit, 12 volt meter that plugs into the cigarette lighter socket.
About $16.00.


Signed: Janitor Tzap

[MrAl]

Hello Janitor,


Well yes, and to read current i would rig another one up to the current sense resistor(s) with a special purpose low VinOffset amplifier. Basic 'movement' could be 200mv as that would work best i think.