Two meters show different amperage

Merry Christmas

gar

Senior Member
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?

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Joey94

Member
Location
Illinois
Occupation
Apprentice
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
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.
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tallgirl

Senior Member
Location
Great White North
Occupation
Controls Systems firmware engineer
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This is what I was able to do with the information I found online about the 555 timer.


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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.
 

gar

Senior Member
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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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
211126-1423 EST

Joey94:

Some references ---




There is also a TI data sheet that pops up.

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Joey94

Member
Location
Illinois
Occupation
Apprentice
211126-1423 EST

Joey94:

Some references ---




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
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.

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gar

Senior Member
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.

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gar

Senior Member
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.

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