Two meters show different amperage

[gar]

211212-2154 EST

Some additional comments.

The pulses produced by the 555 were very consistent for each particular RC combination in the 555 circuit. All the variation in the meter readings are a result of whatever algorithm is being used in the meter.

If you are testing meters I would connect all meters in parallel so that each gets exactly the same pulse as the other meters,

To change this to an AC test connect an ODC5 solid state relay across the 555 output as the relay's input signal.. Load the OAC5 with a small power resistor, or a 15 W incandescent.

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[retirede]

Darned….I was hoping to make the 100th post on this thread, but I missed it!

 

[Joey94]

So I was able to make the output 10V. How do you know the lenght of the pulses? With the oscilloscope? My Klein tools meter as I connect it shows me 100mv without triggering the output.


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[gar]

211214-2112 EST

Joey94:

You use a scope in single shot mode. Use DC input on the a scope Y axis channel. Move the trigger point on the X axis to about 2 major divisions on the X axis from the left side of the screen. Thus, when triggered your displayed pulse which goes positive will start at these two division from the left. Ball parkish I would used DC coupling for trigger from the Y channel being viewed. Use positive slope triggering, Set the trigger even at about 5 V. Place the Y axis trace with 0 input at about 1 or 2 major divisions from the bottom of the screen.

Set the scope time base long enough to see the entire pulse. Pulse width is somewhere near 1 time constant of the timing resistor and capacitor. R in megohms, and C in uff produces a time constant in Seconds. 100k and 0.1 uff is somewhere near a pulse of 0,01 seconds.

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[gar]

211214-2146 EST

My last post has problems. I was working on it when there was some sort of crash, and now I find it posted.

Set the trigger level at about 5 V. Place the Y axis trace with 0 input at about 1 or 2 major divisions from the bottom of the screen.

Set the scope time base long enough to see the entire pulse. Pulse width is somewhere near 1 time constant of the timing resistor and capacitor. R in megohms, and C in ufd produces a time constant in Seconds. 100k and 0.1 ufd is somewhere near a pulse width of 0,01 seconds.

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[gar]

211215-1439 EST

joey94:

I missed your mention of 100 mV. If that was the output voltage of the 555 in its rest state, logic 0 output no pulse, then that can be expected. I will measure my similar state. This is the lowest voltage produced from the output transistor in the 555 device. I believe the 555 uses some form of a totem pole output stage. This means a pulldown transistor is turned on for 0 output, and off for a logic 1, and a pulp transistor is off when the output is logic 0, and is on to pulp when the output is a logic 1.

To some extent this exists in a push-pull audio amplifier, but the two switches are not switches, but are variable resistors.

I believe the TTL logic output was invented in the mid 1960s by TI ( Texas Instruments ) to replace RTL logic to produce greater noise immunity, and provide greater drive capability. The first 7400 circuits were quite expensive. I think it was 1967 when I could first afford to buy a TTL circuit. Before this I did some playing with some Motorola RTL circuits. Somewhere in this time frame the first integrated OP amp became available, about $35 in those days, or possibly $700 in today's money.

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[gar]

211215-1541 EST

Joey94:

With my 555 in its off state, and no load on the output except my Fluke 87 from the output to common the reading is 0.008 V. If from the output to +12 V I place a 10,000 ohm resistor ( in other words inject a current of12/10,000 = 1 mA into the output ) then the output voltage relative to common rises to 26 mV from 8 mV, or a change of 18 mV. Thus, the output impedance at these current levels appears to be about R = 0.018/0.001 = 18 ohms. The TI data sheet shows output voltage low at 50 mA to be 1 V typical and 2 V max. Note: 1/0.05 = 20 ohms. At a much different current level close to my 18 ohms.

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[gar]

211216-1147 EST

Back to some pulse tests on the Fluke 87.

These tests are with a DC pulse. Rest state near 0 V, pulse height is 10V. The Fluke 87 is in DC V mode, and fixed range of 00.000 . It is important that one run tests in a fixed range mode rather than auto-ranging. Three pulse durations were used 40, 60, 100 milliseconds. Scope time base was 20 mS per major division. Scope in single shot mode and used to make sure a test was a single pulse. Ten trials for each of the three pulse widths,

Test results:

40 millisec 10 V positive pulse

5.64, 5.64, 5.60, 5.44, 5.20, 5.28, 5.68, 5.52, 5.64, 5.16
Max = 5.68, Min = 5.16, Ave = 5.46, Max diff = 0.52


60 millisec 10 V positive pulse

7.00, 6.60, 6.24, 6.80, 6.56, 7.00, 6.96, 6.88, 6.12, 6.92
Max = 7.00, Min = 6.12, Ave = 6.71, Max diff = 0.88


100 millisec 10 V positive pulse

9.68, 9.72, 9.36, 9.36, 9.52, 9.32, 9.72, 9.76, 9.28
Max = 9.76, Min = 9.28, Ave = 9.52, Max diff = 0.48

Note that there is considerable variance from one measurement to the next per pulse width.

No data here for the Fluke 27, but it requires much longer pulses to approach a reading close to the pulse height.

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[gar]

211216-1617 EST

Now a test on the Fluke 27. Same conditions as the Fluke 87 above.

100 millisec 10 V positive pulse

3.20, 3.10, 3.08, 3.00, 3.13, 1.44, 3.12, 3.13, 0.67, 3.11, 0.82, 2.25, 2.86
Max = 3.20, Min = 2.25, Max diff = 0.95

The 1.44, 0.67, and 0.82 are not included in my average calculation. They are an indication of potential problems in using this meter without some judgement on the results.

This meter has a much longer averaging time constant than the Fluke 87.

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[gar]

211216-1700 EST

Back to the Fluke 87. This time in PEAK mode, 1 mS.

40 millisec 10 V positive ( actually about 12 V ) pulse

11.88, 11.92, 11.92, 11.88, 11.92, 11.96, 11.96, 12.04, 12.00, 12.00
Max = 12.04, Min = 11.88, Max diff = 0.16


1 millisec same voltage pulse

11.96, 11.92, 11.88, 11.68, 11.80, 11.76, 11.72, 11.72, 11.76, 11.68
Max = 11.96, Min = 11.68, Max diff = 0.28

Slightly greater max diff for 1 millisec, and slightly lower average voltage.

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[Joey94]

First of all Merry Christmas Everyone! Especially to you Gar and thank you so much for all your help.
So I kept trying to make this work but for some reason my Klein Tools meter will only show about 10 mV for anything that has 100 to 300 microseconds.
When I have 18.5ms I get a reading of 0.786 V, 0.354 V, 0.851 V and similar readings with all 3 meters.
Maybe I’m doing something wrong or is it the meter that can’t read such a short period of time?
The oscilloscope shows the voltage of Peak to Peak 11.44V, Top 9.52V, Rms 7.77V


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[gar]

211226-1333 EST

Joey94:

You are experiencing what I might expect. You need to continue the experiment with the Klein meter. As you increase the duration of the pulse you will start to see increased values as the pulse gets longer.

An experiment you might do before this is:

Experimental setup:

1. An adjustable duration single shot DC voltage source of low impedance, for example your 555 timer. Make its output about 10 V. This you already have, and it is working.

2. As a load to the timer connect a diode to a 1 megohm resistor that is then connected to a 1 mfd capacitor that then goes to common. The diode anode is connected to the timer output, and cathode to the 1 meg resistor. A 1N4148 is a good small signal diode to use. A good mylar or polypropylene capacitor is good to use ( low leakage ).

3. Provide a means to short the capacitor after each test. A piece of wire or pushbutton switch will work.

When you charge a capacitor this way the rise in capacitor voltage follows an exponential curve. Thus,
Vc = Vmax * (1 - e exp -t/RC ). For t = RC the equation is Vc = Vmax ( 1 - e exp -1 ). Vc = Vmax ( 1 - e exp -1 ). e exp -1 = 0.3679. Thus, for t = 1 time constant the capacitor voltage is Vc = Vmax * ( 1- 0.3679 } = Vmax * 0.6321. This is commonly known as 1 time constant.

From t = 0 to 1 time constant T the curve is close to linear. From 1 T to 2T it is approximately linear but of a different slope, and continues on as you go to higher time constant segments in the curve.

As you increase the duration of the excitation time to your fixed RC circuit your final voltage will gradually increaseI to its maximum value. In theory the maximum will never be reached in finite time.

Your meter may not act exactly as an exponential curve but will be similar.

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[kwired]

Ahh, I didn't realize that you had them in max mode. I agree with @synchro, and further I don't know what the stated accuracy is of the maximum current capture. Do they even give it? It could be +/- 20% for all we know.

-Hal

might be a time factor involved in the min/max capture features as well

Edit: I see there are many more posts I have not yet read and this may have come up in one way or another

 

[gar]

211227-1505 EST

kwired:

On my Fluke 27 and 87 there is what I will describe as a very long averaging or integrating time in the MIN-MAX mode, and this averaging time constant is different for my two meters. On the 87 which also has a PEAK mode the time to reach near full value is around 1 millisec in PEAK mode. This is useful. Whereas I judge the MIN-MAX capability on my Flukes to be almost useless.

I am suspecting that Joey's meter probably has an even different averaging time.

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[Christophers]

So is there a flaw in the design or software sampling of the CL700 and CL800? Other than autoranging is the 390 a better deal? I still find Flukes overpriced.

 

[ptonsparky]

I'm not going back to read 114 posts. You choose a meter that meets your needs and your budget. That may mean you have several because those needs are based on the project at hand.

 

[gar]

221127-1407 EST

It would be interesting to hear from Joey94 about what he may have learned since his last post.

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[mtnelect]

Could this experiment be completed with an "Adjustable Timer Module", "AND" and "OR" gate circuitry ?

 

[gar]

221128-1550 EST

mtnelect:

To do this experiment you want a means to produce a single pulse. This pulse should be adjustable in duration over a time range that will produce useful results. The steady state output should be close to 0 V. And the pulse amplitude should be a reasonable value, such as 10 V.

AND and ORs alone will not accomplish this.

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