Need some help with my DMM

[Zeke]

I have a GB GDT 200A model. It's a basic 7 function meter. I'm having trouble with the amps reading aspect. I don't even know if it's working as I've made some stupid mistakes not realizing the selection pointer was upside down or opposite of where I thought it was on the dial. I may have smoked it, but some functions seem fine.

When I want to read what I think is a parasitic voltage dram on my 1990 chevy truck, I get (or got) .97 while in the 10A position. I pulled a suspect fuse and am getting another reading, The issue is, I was doing other things and that's when I thought I was checking how much the battery was charged and maybe put the 2 leads across the battery with the pointer somewhere besides DC 20V. But, I also didn't move the positive lead to the amps port. So I don't know if I buggered it up or not. It still does stuff but I haven used the Ohm fuction. It measures AC just fine.

When I got it back to the amp reading scale, I was seeing a reading. It ranges from 2 to 8 with the decimal in different places in accordance with where I have the selector. Other than the 10A position, everything is a factor of 20. 20mA, 200mA and 2000mA.

If I see "8" at 2000mA, is that 160 mA? I think the parameters for this truck allow for 30mA draw at rest.

Sorry for the long post. I wanted to get down as much info as possible.

TIA.

If the truck won't start tomorrow, I'll know something is still pulling the battery down besides the circuit I killed (courtesy lights and some dash displays).

 

[laser3kw]

usually the switch setting indicates the maximum reading. Your "2000ma" is 2000 milliamp or 2 amp. The reference to "10amp" is the max you can read period. If you exceed it you will pop a fuse hidden inside the case. You can replace the fuse if you smoke it.

 

[Zeke]

Well, other than the max read of 10 amps, everything else is in factors of 20. That's what confuses me. If it was a 20A max MM. the number would be the same, the decimal would be in a different place.

If my first reading was .97 on the 10A scale, that's just shy of 1 amp, right? What would that have read on the next setting of 20mA? Other times I was reading, I only saw "1" at the 10 A level. As I worked down, it got more decimal places and it registered 2 to 8 as it fluctuated. Apparently, at the 10A level, 1 is as low as it will read.

But that contradicts my first reading. What did I do to the MM?

 

[0.511MeV]

You have a "3 and a half" digit display on the meter. That is why everything is a multiple of 2. The display has a 1 as the first digit, it can light or not light the numeral 1. The next three digits of the display can show any number. If your display was fully lit it would look like this: 1888.

Hopefully that explains it.

So, it cannot display 2000 mA, it can only go up to 1999 mA before you need to increase the range. It cannot display 20.00 mA, it can only go to 19.99 mA before you need to increase the range. Etc

To measure current, you have to put the meter in series with the circuit. The probes must be connected to the proper inputs on the meter, they are low impedance and fused.

 

[MrMark]

I have a GB GDT 200A model. It's a basic 7 function meter. I'm having trouble with the amps reading aspect. I don't even know if it's working as I've made some stupid mistakes not realizing the selection pointer was upside down or opposite of where I thought it was on the dial. I may have smoked it, but some functions seem fine.

When I want to read what I think is a parasitic voltage dram on my 1990 chevy truck, I get (or got) .97 while in the 10A position. I pulled a suspect fuse and am getting another reading, The issue is, I was doing other things and that's when I thought I was checking how much the battery was charged and maybe put the 2 leads across the battery with the pointer somewhere besides DC 20V. But, I also didn't move the positive lead to the amps port. So I don't know if I buggered it up or not. It still does stuff but I haven used the Ohm fuction. It measures AC just fine.

Putting the meter across a voltage while set up for amps (with the lead in the shunt port) can damage the meter.

When I got it back to the amp reading scale, I was seeing a reading. It ranges from 2 to 8 with the decimal in different places in accordance with where I have the selector. Other than the 10A position, everything is a factor of 20. 20mA, 200mA and 2000mA.

If I see "8" at 2000mA, is that 160 mA? I think the parameters for this truck allow for 30mA draw at rest.


NO. That means out of range or damaged, no doubt. The "1" generally means that the range has been exceeded. In your case, if you saw a "1" that would mean you are reading over 2 amps. The manual ranging just changes the decimal place, allowing you more significant digits of resolution as long as you are below the range. If set to the 2000ma setting, 160mA should read 160.X. Change to 200ma setting and it would read 16.0X, giving you more resolution. Finally, switch to 20ma setting and you should see the "1"

Sorry for the long post. I wanted to get down as much info as possible.

TIA.

If the truck won't start tomorrow, I'll know something is still pulling the battery down besides the circuit I killed (courtesy lights and some dash displays).

ten characters

 

[MrMark]

Although you have your answers putting the last two posts together, you probably should have put this in the tools forum.

BTW, there is a better way to do what you are doing.

You can simply measure the voltage across each fuse top (the pins are accessible) and using a handy table that is available online convert that voltage into current through the fuse. Each fuse rating has a specific resistance that is known. This way you don't have to open up the main battery circuit.

This is why I suggested you move this as it is more of a car tool question than house wiring.

 

[Zeke]

Who said this is house wiring? Electrical is electrical. But, I put it here because this is where the men who understand current are. I don't need a bunch of jackleg answers. The bit about the "1" registering is what I was looking for. And I thank you for your info.

Back to the meter: since I can't find any info on repairing the fuse, I'm going to buy a new meter. This one will be fine in my truck tool box for the other applications. The instructions that came with this are useless.

Oh, and I didn't put the meter across voltage while in the amps setting. What is the "shunt port"?

 

[MoonRise]

DMM - you usually don't have to 'scale' the reading.

analog meter - you have to read the right scale on the meter face and use that to get the right value for what you are reading.

Ammeter typically has to go in-line with the circuit under test. If you have the meter set to read amps and put the test leads/probes right onto a voltage source, you do one of two things. Best result is you smoke an internal fuse. Open up the case and replace fuse and you should be back in business. Worse result is you smoke something internal that is not a fuse, in which case the meter (or that function of themeter) is toast.

MrMark had a typo in his replay above. If the current flow through the circuit was actually 160 ma, in the 2000ma range the meter would read "160.x". In the 200 ma range, the meter would read "160.x". In the 20 ma range, the internal protective fuse may blow (to protect the meter) or the meter may be damaged (bad design of the meter to not have a protective fuse in there).

Your previous reading of "8" in the 2000 ma should be read as "8" ma. Since the current is low, you could change the range selector down to the 200 ma or even 20 ma range and still get that 'same' 8 ma reading (if nothing else kicks in/on electrically, like a dome light or a CPU or anything else).

Often on the 'little' meters, they have two 'standard' test lead ports for everything except the 'highest amp' setting (10 amp in your case). To use that 'special' high(er) amp setting on the meter, you usually have to remove one test lead out of its 'standard' port and put it into the 'special' 10A port. This sends the (possibly) higher amperage you are testing through slightly different circuits in the meter but more importantly should send the current through a higher amperage (10A, in this case) protection fuse.

To change the fuse, usually you have to remove the battery cover and/or the case back of the meter and then just replace the burned-out fuse(s).

 

[MoonRise]

the 'shunt port' is the 'special' high(er) amperage port you have to use to for the (in this case) 10A ammeter setting.

 

[Zeke]

Gottcha. But are you saying I can read safe, low amperages with the leads in the normal position? When I put the selector to any amp setting and the leads are in the normal position, the meter just starts reading random numbers. That was yesterday. Today, the meter zeros out and stays there. I have a new battery in it, but I figured that was for Ohms, continuity and maybe the temp probe. Oh, I guess it powers the hFE function.

I'll never use that, but I bet I had the selector there by accident as it's opposite the 20 DCV position and I don't always see the little dot indicting the correct end of the pointer. Bad design.

 

[alan_3301]

You can simply measure the voltage across each fuse top (the pins are accessible) and using a handy table that is available online convert that voltage into current through the fuse. Each fuse rating has a specific resistance that is known. This way you don't have to open up the main battery circuit.

This is the best way to measure parasitic draw in autos, and I have been doing it this way for years. I'm not sure how many computers are in your vehicle, but usually when power is disconnected and reconnected they take a while to power back down into sleep mode. Pulling fuses and putting them back in while checking the amp reading can get confusing because of this, the modules take time to settle down. If it's a light or motor that stays on it's not an issue, but easier to skip this problem altogether.

The only time this wont work is when the draw is on an unfused circuit, starter or alternator for example.

Here is a link that explains the whole procedure. It's published for VWs but applies to everything.

https://wiki.bentleypublishers.com/...rough+fuse+panel+VW+technical+bulletin+270711

 

[MoonRise]

Gottcha. But are you saying I can read safe, low amperages with the leads in the normal position? When I put the selector to any amp setting and the leads are in the normal position, the meter just starts reading random numbers. That was yesterday. Today, the meter zeros out and stays there. I have a new battery in it, but I figured that was for Ohms, continuity and maybe the temp probe. Oh, I guess it powers the hFE function.

I'll never use that, but I bet I had the selector there by accident as it's opposite the 20 DCV position and I don't always see the little dot indicting the correct end of the pointer. Bad design.

With all the various DMM I've used/seen (but not specifically a GB GDT200A DMM), yes.

The 'low' amperage readings are done with the test probes in the 'regular' ports, and when you want/need to use the 'high' amperage range you then just switch the one probe into that 'special' high-amp port.

As usual, RTFM (or at least the label) to know how to use the different ranges and ports on the DMM.

As to the DMM 'bouncing' around in its low-amperage readings yesterday and now just showing a big fat and steady "0", it sounds like you smoked the fuse. Open up the battery compartment and/or the case back and check the fuses in there. On those 'little' meters, there are usually two. One general one and one 'high-amp' one. Replace burned-out fuse (with the correct amp rating!!!) and put the meter back together. Should be back in business then.

Unless you are just looking for an excuse to go out and buy a new DMM.

 

[MrMark]

Who said this is house wiring? Electrical is electrical. But, I put it here because this is where the men who understand current are. I don't need a bunch of jackleg answers. The bit about the "1" registering is what I was looking for. And I thank you for your info.

Back to the meter: since I can't find any info on repairing the fuse, I'm going to buy a new meter. This one will be fine in my truck tool box for the other applications. The instructions that came with this are useless.

Oh, and I didn't put the meter across voltage while in the amps setting. What is the "shunt port"?

Last time I ever help you, what a smartass. Come to a forum hat in hand and someone takes the time to give you a fairly advanced answer and this is the reward.

 

[Zeke]

With all the various DMM I've used/seen (but not specifically a GB GDT200A DMM), yes.

The 'low' amperage readings are done with the test probes in the 'regular' ports, and when you want/need to use the 'high' amperage range you then just switch the one probe into that 'special' high-amp port.

As usual, RTFM (or at least the label) to know how to use the different ranges and ports on the DMM.

As to the DMM 'bouncing' around in its low-amperage readings yesterday and now just showing a big fat and steady "0", it sounds like you smoked the fuse. Open up the battery compartment and/or the case back and check the fuses in there. On those 'little' meters, there are usually two. One general one and one 'high-amp' one. Replace burned-out fuse (with the correct amp rating!!!) and put the meter back together. Should be back in business then.

Unless you are just looking for an excuse to go out and buy a new DMM.

It says in post #1 that it's a 1990 Chevy truck. OBDI and not much of an ECU. The only draw after shutting down is the fuel pump for 10 seconds.

I did another kind of check, since my meter was acting up. I pulled the fuses one by one in the dark and found the interior lights was the culprit as it sparked on reconnection. I had the doors closed and I don't have any delays on those lights like modern cars. The glove box light goes out, there is no trunk light and no lights in the doors to illuminate the threshold and entry. My display went out but cam back this morning with the fuse still out.

So, something is not right. But, I'll start a thread on that in Free Parking or over on the truck forum.

 

[nanofrog]

Gottcha. But are you saying I can read safe, low amperages with the leads in the normal position? When I put the selector to any amp setting and the leads are in the normal position, the meter just starts reading random numbers. That was yesterday. Today, the meter zeros out and stays there. I have a new battery in it, but I figured that was for Ohms, continuity and maybe the temp probe. Oh, I guess it powers the hFE function.

I'll never use that, but I bet I had the selector there by accident as it's opposite the 20 DCV position and I don't always see the little dot indicting the correct end of the pointer. Bad design.

What do you mean by "leads in the normal position"?

I presume you mean the V(Ohm)mA jack, and you've set the range accordingly (start high <200m setting under DCA> if you're not sure, then move through smaller values), you should get a proper reading.

If not, that meter is trash (not exactly uncommon with these, as they're the cheapest DMM's ever made, and rebranded under countless names), and needs to be replaced.

As per the indicator dial, you could put a drop of nail polish or testors model paint in the recessed hole for a better visual indicator for the range switch (lots of meters can use this trick IMHO).

 

[BrewSperkey]

I think this short video will help clear things up...