Two meters show different amperage
- Thread starter Joey94
- Start date
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211123-1052 EST
Joey94:
I have been thinking on how you might setup a test to evaluate meters.
I keep returning to the use of an NE555 timer integrated circuit as as the basic means to generate a controlled duration signal. I also believe the first tests should be to generate a DC pulse and study the meter DC response. Once you have worked with DC signals, then that same DC pulse generator can be used to control an SCR or Triac AC switch.
I have searched the Internet for what might be a useful 555 kit or prebuilt pulse generator. I have found a lot of useless results. So it may mean you need to start from scratch. What you broadly need is a monostable ( single shot ) circuit switching an approximately 12 V source ( a 12 V battery ) with a timing range of about 10 microseconds to 10 seconds. You want to produce an output voltage pulse of about 10 V. In other words 0 V most of the time. Whether the pulse is positive or negative does not matter.
Additionally you want a way to pulse the pulse generator. This can be a manual pushbutton or a repetitive pulse generator that has a slow enough pulse rate that you can reset your meter under test between the pulses.
Do you have any experience working with electronic components?
.
Joey94:
I have been thinking on how you might setup a test to evaluate meters.
I keep returning to the use of an NE555 timer integrated circuit as as the basic means to generate a controlled duration signal. I also believe the first tests should be to generate a DC pulse and study the meter DC response. Once you have worked with DC signals, then that same DC pulse generator can be used to control an SCR or Triac AC switch.
I have searched the Internet for what might be a useful 555 kit or prebuilt pulse generator. I have found a lot of useless results. So it may mean you need to start from scratch. What you broadly need is a monostable ( single shot ) circuit switching an approximately 12 V source ( a 12 V battery ) with a timing range of about 10 microseconds to 10 seconds. You want to produce an output voltage pulse of about 10 V. In other words 0 V most of the time. Whether the pulse is positive or negative does not matter.
Additionally you want a way to pulse the pulse generator. This can be a manual pushbutton or a repetitive pulse generator that has a slow enough pulse rate that you can reset your meter under test between the pulses.
Do you have any experience working with electronic components?
.
I do have some experience. Not too much. I’ve been playing around with breadboards and I got myself a dc power supply, function generator, oscilloscope and soldering station to do some testing and learning. I have an electronic component assortment kit which includes NE555P.
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211123-2214 EST
Joey94:
That is great. You have most of what you need to start playing. I want you to start with a supply voltage of about 10 to 12 V DC, but 5 V would work. Next you need the components to mock up a single shot 555 timer. A circuit diagram for this single shot mode can be found at the Signetics data sheet for the 555. Do an Internet search and print out the data sheet.
For the timing components start with a 100k to 500k variable resistor in series with 2k. This makes the minimum timing resistance 2k. As a first capacitor to use for timing use an 0.001 mfd unit. Use mica, or polypropylene capacitors.
With a 2k minimum resistance and maximum of about 102k I get a pulse width from about 20 microseconds about 1200 microseconds.
If you trigger this circuit from a 0.25 to 0.1 Hz rep rate pulse, the you will have time to reset your single shot scope between pulses. This also is a means to provide sufficient time between pulses to reset the meter that is monitoring the pulse. Otherwise you manually trigger the single shot.
See if you can create this experiment.
.
Joey94:
That is great. You have most of what you need to start playing. I want you to start with a supply voltage of about 10 to 12 V DC, but 5 V would work. Next you need the components to mock up a single shot 555 timer. A circuit diagram for this single shot mode can be found at the Signetics data sheet for the 555. Do an Internet search and print out the data sheet.
For the timing components start with a 100k to 500k variable resistor in series with 2k. This makes the minimum timing resistance 2k. As a first capacitor to use for timing use an 0.001 mfd unit. Use mica, or polypropylene capacitors.
With a 2k minimum resistance and maximum of about 102k I get a pulse width from about 20 microseconds about 1200 microseconds.
If you trigger this circuit from a 0.25 to 0.1 Hz rep rate pulse, the you will have time to reset your single shot scope between pulses. This also is a means to provide sufficient time between pulses to reset the meter that is monitoring the pulse. Otherwise you manually trigger the single shot.
See if you can create this experiment.
.
tallgirl
Senior Member
- Location
- Great White North
- Occupation
- Controls Systems firmware engineer
Congratulations. You've progressed to where I was when I was maybe 15 or 16. If you keep it up you can follow in my footsteps and start programming our robot overlords.
This is what I was able to do with the information I found online about the 555 timer.
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211125-1655 EST
Joey94:
To make the 555 a single shot device you supply DC ( 5 to12 V ) power between pins 8 and 1 with 1 being connected to battery minus and 8 connect to the plus. Put a capacitor of possibly 5 to 25 mfd across this DC supply near the 555. This is just an AC short near the 555.
Connect pin 8 ( your + supply voltage ) to pin 4 to hold 4 high.
For single shot mode pins 6 and 7 are connected together, and your timing resistor and capacitor are connected here. The timing resistor needs a minimum value of possibly 2k, and for the standard 555 vs CMOS about 500k maximum. The other end of the timing resistor goes to pin 8 the plus supply. The other capacitor end goes to pin 1 the minus or common supply point.
Do not connect anything to pin 5.
Pin 3 is the output pulse.
Connect a 10k resistor from plus supply to pin 2 the trigger pin. This biases pin 2 high.
Connect an 0.002 mfd capacitor to pin 2 to couple in a trigger pulse. Connect the free end of the trigger capacitor thru a 1 Meg resistor to pin 8, your plus supply voltage. Under steady state conditions this puts 0 charge on the trigger capacitor. Pulling the 1 Meg end of the trigger capacitor to common ( minus ) produces a negative pulse into pin 2 triggering the single shot.
The company data sheet you are looking for is Signetics.
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Joey94:
To make the 555 a single shot device you supply DC ( 5 to12 V ) power between pins 8 and 1 with 1 being connected to battery minus and 8 connect to the plus. Put a capacitor of possibly 5 to 25 mfd across this DC supply near the 555. This is just an AC short near the 555.
Connect pin 8 ( your + supply voltage ) to pin 4 to hold 4 high.
For single shot mode pins 6 and 7 are connected together, and your timing resistor and capacitor are connected here. The timing resistor needs a minimum value of possibly 2k, and for the standard 555 vs CMOS about 500k maximum. The other end of the timing resistor goes to pin 8 the plus supply. The other capacitor end goes to pin 1 the minus or common supply point.
Do not connect anything to pin 5.
Pin 3 is the output pulse.
Connect a 10k resistor from plus supply to pin 2 the trigger pin. This biases pin 2 high.
Connect an 0.002 mfd capacitor to pin 2 to couple in a trigger pulse. Connect the free end of the trigger capacitor thru a 1 Meg resistor to pin 8, your plus supply voltage. Under steady state conditions this puts 0 charge on the trigger capacitor. Pulling the 1 Meg end of the trigger capacitor to common ( minus ) produces a negative pulse into pin 2 triggering the single shot.
The company data sheet you are looking for is Signetics.
.
ptonsparky
Tom
- Occupation
- EC - retired
Well that is encouraging!
tallgirl
Senior Member
- Location
- Great White North
- Occupation
- Controls Systems firmware engineer
Well that is encouraging!
I started screwing around with electronics in '74, with a lot of very basic circuits. Today I'm programming our robot overlords. Some day I'll find the lighting controller for my building floor and I'll program it to turn the damned lights on whenever it recognizes that I'm in the building on a day off like I'll be in a few hours.
In all seriousness, as buildings get smarter the industry needs more people who understand how structures actually behave. If he can pick up how controls work, a future doing what i do for a living could be very rewarding.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211126-1423 EST
Joey94:
Some references ---
spectrum.ieee.org
There is also a TI data sheet that pops up.
.
Joey94:
Some references ---
Chip Hall of Fame: Signetics NE555
A humble timer chip that became the Swiss Army knife of countless circuits
spectrum.ieee.org
LM555 PDF
Part #: LM555. Description: Single Timer. File Size: 473.19 Kbytes. Manufacturer: ON Semiconductor.
pdf1.alldatasheet.com
There is also a TI data sheet that pops up.
.
211126-1423 EST
Joey94:
Some references ---
Chip Hall of Fame: Signetics NE555
A humble timer chip that became the Swiss Army knife of countless circuits
LM555 PDF
Part #: LM555. Description: Single Timer. File Size: 473.19 Kbytes. Manufacturer: ON Semiconductor.pdf1.alldatasheet.com
There is also a TI data sheet that pops up.
.
Is this correct ?
I pin 8 to positive pin 1 to negative.
I added a 22 mfd across positive and negative for AC short.
I connected pin 8 to pin 4
Pin 6 is connected to 7
The timing resistor is connected between pin 6-7-8 have the single leg at pin 7 and the two at 6-8
It has about 2k min minimum and 500k maximum
Nothing connected to Pin 5
I put my probe to pin 3 output
I have a 10k resistor from my positive to pin 2
0.002 mfd from pin 2 to pin 8 through a 1 Meg resistor.
Let me know if I got this wrong.
Thank you!
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211127-2343 EDT
Joey94:
The best I see and guess at what bus bars are it lookslikenyou have correctly wired the circuit.
I believe your description is slightly incorrect ---
"The timing resistor is connected between pin 6-7-8"
Should read something like Timing Resistor is connected between Pin 8 ( + supply ), and Pins 6 and 7 connected together, Timing Capacitor is connected between Pin 1 ( common ), and Pins 6 and 7 connected together. This appears how you have wired the circuit.
I can not see enough of your layout to be sure.
.
Joey94:
The best I see and guess at what bus bars are it lookslikenyou have correctly wired the circuit.
I believe your description is slightly incorrect ---
"The timing resistor is connected between pin 6-7-8"
Should read something like Timing Resistor is connected between Pin 8 ( + supply ), and Pins 6 and 7 connected together, Timing Capacitor is connected between Pin 1 ( common ), and Pins 6 and 7 connected together. This appears how you have wired the circuit.
I can not see enough of your layout to be sure.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
212227-2432 EST
Joey94:
You should expect the output voltage from pin 3 to be close to 0 v until you pulse the chip.
You pulse the chip by momentarily taking the input side of the trigger capacitor to common. This produces a negative pulse at Pin 2 from the positive supply voltage where the capacitor was biased down to common. Thus. triggering the chip.
.
Joey94:
You should expect the output voltage from pin 3 to be close to 0 v until you pulse the chip.
You pulse the chip by momentarily taking the input side of the trigger capacitor to common. This produces a negative pulse at Pin 2 from the positive supply voltage where the capacitor was biased down to common. Thus. triggering the chip.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211127-2501 EST
Joey94:
See
”1. Monostable Operation” at https://pdf1.alldatasheet.com/datasheet-pdf/view/1068528/ONSEMI/LM555.html
.
Joey94:
See
”1. Monostable Operation” at https://pdf1.alldatasheet.com/datasheet-pdf/view/1068528/ONSEMI/LM555.html
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211127-2653 EST
Joey94:
Do you know what the words "single shot multivibrator" or "monostable multivibrator" mean?
These words refer to some device that produces a timed single pulse from a single trigger pulse.
In the case of a 555 timer a negative slope trigger pulse ( the negative slope ) is the triggering function. This initiates a positive pulse output. In turn the trailing negative slope of the positive output pulse can be used as a trigger for a next stage of another pulse generation that starts its output at the trailing edge of the first pulse generator. As many of these delays can be cascaded together as desired.
.
Joey94:
Do you know what the words "single shot multivibrator" or "monostable multivibrator" mean?
These words refer to some device that produces a timed single pulse from a single trigger pulse.
In the case of a 555 timer a negative slope trigger pulse ( the negative slope ) is the triggering function. This initiates a positive pulse output. In turn the trailing negative slope of the positive output pulse can be used as a trigger for a next stage of another pulse generation that starts its output at the trailing edge of the first pulse generator. As many of these delays can be cascaded together as desired.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211210-2020 EST
Joey94:
Have you been able to get the 555 operational in the single shot mode and make single shot displays on the scope?
.
Joey94:
Have you been able to get the 555 operational in the single shot mode and make single shot displays on the scope?
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211212-1133 EST
Joey94:
Now you are close to being able to make some meter measurements. I am going to suggest DC first.
If I provide a power supply that is adjustable so as to be able to produced a switched 10 V pulse, then I can run an experiment without calculations. I can I do this? If you do not have an adjustable supply, then use a 12 V battery as the source.
We want a switched source that will produce a 10 V pulse. Because you meter under test is a high input impedance device a pulse source of 1 K ohms should be OK. We can use a 1 K 1/2 W resistor as our pulse voltage source as follows:
When your 555 timer is pulsed it produces a + pulse relative to common that almost swings between 0 and the + supply voltage to the 555. So the easy way to create the pulse is to directly use the pulse from the 555. So supply the 555 circuit from a 12 V battery. Then place a voltage divider as a load on the 555 between common and the 555 timer output of a 1K fixed and a variable 250 ohm adjustable resistor.. This should allow you to adjust the output pulse to 10 V.
Once you can produce the 10 V pulse, then you can connect the meter under test across the 1 K resistor an run experiments at different pulse durations. Playing with my Fluke meters I found it necessary to effectively reset MAX or PEAK hold after each pulse test. There is no reset button on the Flukes.
See what happens. I have not run the test yet.
.
Joey94:
Now you are close to being able to make some meter measurements. I am going to suggest DC first.
If I provide a power supply that is adjustable so as to be able to produced a switched 10 V pulse, then I can run an experiment without calculations. I can I do this? If you do not have an adjustable supply, then use a 12 V battery as the source.
We want a switched source that will produce a 10 V pulse. Because you meter under test is a high input impedance device a pulse source of 1 K ohms should be OK. We can use a 1 K 1/2 W resistor as our pulse voltage source as follows:
When your 555 timer is pulsed it produces a + pulse relative to common that almost swings between 0 and the + supply voltage to the 555. So the easy way to create the pulse is to directly use the pulse from the 555. So supply the 555 circuit from a 12 V battery. Then place a voltage divider as a load on the 555 between common and the 555 timer output of a 1K fixed and a variable 250 ohm adjustable resistor.. This should allow you to adjust the output pulse to 10 V.
Once you can produce the 10 V pulse, then you can connect the meter under test across the 1 K resistor an run experiments at different pulse durations. Playing with my Fluke meters I found it necessary to effectively reset MAX or PEAK hold after each pulse test. There is no reset button on the Flukes.
See what happens. I have not run the test yet.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
211212-1656 EST
I have run some tests that will illustrate some of the problems that Joey94 originally encountered. This should provide Joey and some others a little guidance in understanding and running their own future experiments.
My test signal was a 10 V positive rectangular single shot pulse.
This pulse was obtained from a 555 timer circuit. The 555 had a 12 VDC battery as its power source. Battery voltage was somewhat above 12 V.
Different RC time constants were provided br a variable resistance, minimum 2 K, and several fixed Myler capacitors. A 10 V pulse output was obtained from a 5 K Heliport across the output terminal to common.
Two meters were simultaneously tested, a Fluke 87, and a 27. The meters were in parallel across the lower portion of the Heliport. Only the 87 was tested with the shortest pulses. Four tests were run for each pulse duration. The pulse readings have considerable variance. This results from the way the meter is designed. The measurements are averaged to provide a single value, and the min-max difference is also listed.
Avg ...... peak to peak diff
0.044 ---- 0.084 ----- 100 microsec
0.077 ---- 0.102 ----- 300 microsec
0.158 ---- 0.144 ----- 600 microsec
0.159 ---- 0.132 ----- 1 millisec
0.381 ---- 0.467 ----- 1 millisec 87
0.057 ---- 0.056 ----- 1 millisec 27
0.390 ---- 0.036 ----- 3 millisec 87
0.073 ---- 0.083 ----- 3 millisec 27
1.524 ---- 0.353 ----- 10 millisec 87
0.353 ---- 0.676 ----- 10 millisec 27
3.632 ---- 0.210 ----- 30 millisec 87
0.757 ---- 0.700 ----- 30 millisec 27
7.930 ---- 0.068 ----- 100 millisec 87
2.065 ---- 1.210 ----- 100 millisec 27
There is considerable more variability in the measurements than I might have ex[pected.
The Fluke 87 in its pulse mode is much faster. I have shown no data for that here.
.
I have run some tests that will illustrate some of the problems that Joey94 originally encountered. This should provide Joey and some others a little guidance in understanding and running their own future experiments.
My test signal was a 10 V positive rectangular single shot pulse.
This pulse was obtained from a 555 timer circuit. The 555 had a 12 VDC battery as its power source. Battery voltage was somewhat above 12 V.
Different RC time constants were provided br a variable resistance, minimum 2 K, and several fixed Myler capacitors. A 10 V pulse output was obtained from a 5 K Heliport across the output terminal to common.
Two meters were simultaneously tested, a Fluke 87, and a 27. The meters were in parallel across the lower portion of the Heliport. Only the 87 was tested with the shortest pulses. Four tests were run for each pulse duration. The pulse readings have considerable variance. This results from the way the meter is designed. The measurements are averaged to provide a single value, and the min-max difference is also listed.
Avg ...... peak to peak diff
0.044 ---- 0.084 ----- 100 microsec
0.077 ---- 0.102 ----- 300 microsec
0.158 ---- 0.144 ----- 600 microsec
0.159 ---- 0.132 ----- 1 millisec
0.381 ---- 0.467 ----- 1 millisec 87
0.057 ---- 0.056 ----- 1 millisec 27
0.390 ---- 0.036 ----- 3 millisec 87
0.073 ---- 0.083 ----- 3 millisec 27
1.524 ---- 0.353 ----- 10 millisec 87
0.353 ---- 0.676 ----- 10 millisec 27
3.632 ---- 0.210 ----- 30 millisec 87
0.757 ---- 0.700 ----- 30 millisec 27
7.930 ---- 0.068 ----- 100 millisec 87
2.065 ---- 1.210 ----- 100 millisec 27
There is considerable more variability in the measurements than I might have ex[pected.
The Fluke 87 in its pulse mode is much faster. I have shown no data for that here.
.
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