Hi guys,
I am searching for a simple digital panel meter like these:
Blue DC0-500V LCD Digital Volt Panel Meter/Voltmeter New - UK seller | eBay
LED Digital Voltage Meter Voltmeter Panel DC 4.5~30V Small Mini Blue Portable | eBay
Digital-Panelmeter PM438 Panel-Meter PM438 | eBay
They are probably all based on the same chipset anyway.
The thing is, I want to measure a few volts negative to the power supply ground. I believe these panel meters have floating inputs, so should be possible, but I cannot find any information on the negative common mode for the input.
Any of you have experience with these and/or know the allowed input CM?
Edit: some descriptions say something like: power supply 3-12V - must be galvanically isolated from measurement voltage. But that does not say anything about allowed CM range for the measurement input.
tia,
Jan
I am searching for a simple digital panel meter like these:
Blue DC0-500V LCD Digital Volt Panel Meter/Voltmeter New - UK seller | eBay
LED Digital Voltage Meter Voltmeter Panel DC 4.5~30V Small Mini Blue Portable | eBay
Digital-Panelmeter PM438 Panel-Meter PM438 | eBay
They are probably all based on the same chipset anyway.
The thing is, I want to measure a few volts negative to the power supply ground. I believe these panel meters have floating inputs, so should be possible, but I cannot find any information on the negative common mode for the input.
Any of you have experience with these and/or know the allowed input CM?
Edit: some descriptions say something like: power supply 3-12V - must be galvanically isolated from measurement voltage. But that does not say anything about allowed CM range for the measurement input.
tia,
Jan
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The links don't all show meters built from the same chipset. The LED (middle link) one takes power from the voltage being measured, hence the minimum input voltage spec of 4.5V. This one can certainly be connected with red to your power supply GND and measure a negative voltage (between -4.5 and -30V) on its black wire.
So what's the voltage range you need to measure?
So what's the voltage range you need to measure?
I need it for an on-board meter for the regulated 2.1kV power supplies for the direct drive ESL amp ;-)
The design is such that power is available pos to ground while the HV is negative to ground. Due to power requirements I need an LCD, not LED/not backlighted.
But I did find some info on chipsets that presumably are used in such meters, and they apparently have an onboard DC/DC converter that generates a neg supply voltage. So that enables them to measure a voltage negative wrt ground, while powered from a pos voltage wrt ground.
Brighton in the US has what I need, I am waiting for price info but they appear at least 8 x as expensive as the eBay stuff. This IS a hobby, after all.
Jan
The design is such that power is available pos to ground while the HV is negative to ground. Due to power requirements I need an LCD, not LED/not backlighted.
But I did find some info on chipsets that presumably are used in such meters, and they apparently have an onboard DC/DC converter that generates a neg supply voltage. So that enables them to measure a voltage negative wrt ground, while powered from a pos voltage wrt ground.
Brighton in the US has what I need, I am waiting for price info but they appear at least 8 x as expensive as the eBay stuff. This IS a hobby, after all.
Jan
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For that kind of money I think I'd buy a cheap DVM and gut it. You'll know what you have and specs should be available.
No panel-meter without an internal converter is able to cope with significant voltages outside the power supply range (and many have a restricted subrange within that range), but high(er?)-end ones can sense up to -200mV.
They are the ones with a single 5V supply, and the supply common is the same as the input common, unlike the cheapest, 9V battery supplied ones.
I think I still have one or two examples in my stock, I'll try to dig them out to find the manufacturer.
The -200mV can be converted to any arbitrary range with an external divider, of course.
That said, using reasonably clever charge-pump/zener arrangements, even the lowest-cost DPM can be taught to do almost anything.
In the projects I have published, there are probably some examples to be found
They are the ones with a single 5V supply, and the supply common is the same as the input common, unlike the cheapest, 9V battery supplied ones.
I think I still have one or two examples in my stock, I'll try to dig them out to find the manufacturer.
The -200mV can be converted to any arbitrary range with an external divider, of course.
That said, using reasonably clever charge-pump/zener arrangements, even the lowest-cost DPM can be taught to do almost anything.
In the projects I have published, there are probably some examples to be found
I'd buy qty=3 of the EUR_6,49 meters and perform some lab experiments. It's quite possible that the two inputs are electrically isolated and can withstand a voltage difference of 100 volts before something arcs over.
I have some of those in a bin somewhere, they share rougly the same design. They are sold in 200mV base input. I've abused a couple, and they will survive most of what you throw at them if you use a high value divider. (2K per volt or up) the IC features internal protection diodes if i remember correctly. and the decimal point can be set with a blob of solder.
They measure negative and positive inputs, the chipset on them allows measurements up to -200mV. On board resistors are used to scale the input, however for your application I'd keep those off the board as a 0805 resistor can only handle 50 odd volts.
They measure negative and positive inputs, the chipset on them allows measurements up to -200mV. On board resistors are used to scale the input, however for your application I'd keep those off the board as a 0805 resistor can only handle 50 odd volts.
Thank guys, that is helpfull.
Indeed, the 9V battery ones can do that but having a bunch of batteries in the equipment is a nuisance. These are the ones that often have in the spec: 'power supply should be galvanically isolated from the measurement circuit'.
I also found that some of the ones that require 5V do not allow negative measurements, but some of the more expensive ones appear to have an onboard charge-pump to generate an internal negative supply, and they WILL handle negative measurements, usually up to a volt or so.
Brighton from the USA has some but quoted $ 120 + shipping each....
I have ordered a few from a German eBay seller, and will see what they can and cannot do; not all specs are cristal clear...
v4lve lover, I'd appreaciate a ref for those units you mentioned, if you find them.
Jan
Indeed, the 9V battery ones can do that but having a bunch of batteries in the equipment is a nuisance. These are the ones that often have in the spec: 'power supply should be galvanically isolated from the measurement circuit'.
I also found that some of the ones that require 5V do not allow negative measurements, but some of the more expensive ones appear to have an onboard charge-pump to generate an internal negative supply, and they WILL handle negative measurements, usually up to a volt or so.
Brighton from the USA has some but quoted $ 120 + shipping each....
I have ordered a few from a German eBay seller, and will see what they can and cannot do; not all specs are cristal clear...
v4lve lover, I'd appreaciate a ref for those units you mentioned, if you find them.
Jan
All the units I have are based on the ICL7107, quite a good IC, however meas - is tied to the power gnd. The IC will hapily measure -200mV on its positive
I should have a pair of old 2.5Kv scale moving coil meters somewhere. If size is no objection.
I should have a pair of old 2.5Kv scale moving coil meters somewhere. If size is no objection.
If you want full steampunk, I have a couple of electrostatic voltmeters around (>10**15 Ohms input R)
Jan, i saw that you and mark did some lab experiments couple of years ago with this little Chinese panel meter. I am dealing with those now. Do you have any results to share ? this is what i came with after some test, but i am not sure if this is right.
The 12V are separate with a DC/DC power for each.
The 12V are separate with a DC/DC power for each.
Measurement input GND typically is galvanically connected with power GND in all meters.
But there are similar meters with isolated power supply, you may find them by this key word ("isolated"). They have isolated DC/DC onboard, so they cost a bit more.
But there are similar meters with isolated power supply, you may find them by this key word ("isolated"). They have isolated DC/DC onboard, so they cost a bit more.
Thanks Vovk, do you have any example ??
Following Gustav Kirchhoff’s Current Law.
1A of current on the positive side - 1A of current on the negative side, and the ampmeter on the GND wire will read 0A.
Each ampmeter work with separate GND, as soon as i connect both GND together, i read 0A on the positive meter
I needs to find some meters that can be installed on the + and - wires.
Following Gustav Kirchhoff’s Current Law.
1A of current on the positive side - 1A of current on the negative side, and the ampmeter on the GND wire will read 0A.
Each ampmeter work with separate GND, as soon as i connect both GND together, i read 0A on the positive meter
I needs to find some meters that can be installed on the + and - wires.
See the circuits used in the 830B series meters.
The basic idea is that the voltage is 200 mV full scale, and the other values are scaled from it, by using resistors in series for ohms and volts, and in parallel for the current ranges.
So if you want a meter for current, just see what resistors are used.
Cheap voltmeters here are available, mains powered, about the size of a watch, they read volts directly, so only two wires to connect for use as mains voltage meter. That is the supply volts too.
$3 price range here.
Panel meters, properly made as indicators, are about $10 - 12, the amp meters need an external current transformer, which is extra.
The basic idea is that the voltage is 200 mV full scale, and the other values are scaled from it, by using resistors in series for ohms and volts, and in parallel for the current ranges.
So if you want a meter for current, just see what resistors are used.
Cheap voltmeters here are available, mains powered, about the size of a watch, they read volts directly, so only two wires to connect for use as mains voltage meter. That is the supply volts too.
$3 price range here.
Panel meters, properly made as indicators, are about $10 - 12, the amp meters need an external current transformer, which is extra.
https://rishabh.co.in/products/17/digital-panel-meter
https://www.mecoinst.com/meco-products/Digital-Panel-Meters-and-Modules.aspx
https://www.electronicscomp.com/dig...MIzqjAzen_9QIVUddMAh06WAJkEAQYASABEgK1hvD_BwE
The first two are reputed Indian manufacturers.
Rishabh claims to be the world's biggest moving coil meter maker, they have some links to UK companies.
https://www.mecoinst.com/meco-products/Digital-Panel-Meters-and-Modules.aspx
https://www.electronicscomp.com/dig...MIzqjAzen_9QIVUddMAh06WAJkEAQYASABEgK1hvD_BwE
The first two are reputed Indian manufacturers.
Rishabh claims to be the world's biggest moving coil meter maker, they have some links to UK companies.
thanks Nares,
i found this one DC Meter 100V -200~+200A Bidirectional Current Shunt Can be Put On Positive Side
I will try and report...
i found this one DC Meter 100V -200~+200A Bidirectional Current Shunt Can be Put On Positive Side
I will try and report...