Is joule thief circuit gets overunity?

[picowatt]

Can you borrow an analog scope? If so, check your current trace and let us know what you find.

.99,

Sorry.  In my previous post I referred to that formula as the "DC offset spec".

I meant to say "DC measurement accuracy".

Here are the specs again:



DC measurement accuracy:

±[3%X（|reading|+|offset|）+1% of |offset|+0.2div+2mv]


DC gain accuracy:

≤±3.0%: 5mv/div to 5V/div in Fixed Gain Ranges
≤±4.0%:typical for 2mv/div and Variable Gain Ranges

There really is no "offset spec" per se, other than inferred by the DC measurement accuracy.

PW

[poynt99]

PW,

For interest sake, the Tek DPO4054 spec sheet states "±1.5%, derated at 0.10%/°C above 30 °C" for DC Gain accuracy.

[picowatt]

PW,

For interest sake, the Tek DPO4054 spec sheet states "±1.5%, derated at 0.10%/°C above 30 °C" for DC Gain accuracy.

.99,

I saw that in your scope's manual.

In this spec:

DC measurement accuracy:

±[3%X（|reading|+|offset|）+1% of |offset|+0.2div+2mv]

Assuming the term "offset" is the distance the trace is positioned relative to the graticule center, and the way the above is written, would you read that last part "+0.2div+2mv" as separate from the preceding "1% of [offset]" expression?

That is, with the vert sensitivity set to 20mv/div, does "+0.2div+2mv"  actually, all by itself, add +/-6mv to the accuracy spec? (.2x20mv+2mv).  Possibly they dropped a bracket or two as a typo, but I checked several different manuals for a few models and all were written as above.

If that does indeed add +/-6mv by itself, by the time one adds in the rest of the expression and throws in the DC gain error spec as well, 12-14mv may not be all that far out of spec.

PW

ADDED:  Also, Lawrence should check to see if he has the latest firmware installed.  I read somewhere aout an issue with these scopes llocking up or doing something wierd when the "power on cal" reached the offset portion of that procedure.  A firmware update was issued which was supposed to correct the problem.

[ltseung888]

.99,

I saw that in your scope's manual.

In this spec:

DC measurement accuracy:

±[3%X（|reading|+|offset|）+1% of |offset|+0.2div+2mv]

Assuming the term "offset" is the distance the trace is positioned relative to the graticule center, and the way the above is written, would you read that last part "+0.2div+2mv" as separate from the preceding "1% of [offset]" expression?

That is, with the vert sensitivity set to 20mv/div, does "+0.2div+2mv"  actually, all by itself, add +/-6mv to the accuracy spec? (.2x20mv+2mv).  Possibly they dropped a bracket or two as a typo, but I checked several different manuals for a few models and all were written as above.

If that does indeed add +/-6mv by itself, by the time one adds in the rest of the expression and throws in the DC gain error spec as well, 12-14mv may not be all that far out of spec.

PW

ADDED:  Also, Lawrence should check to see if he has the latest firmware installed.  I read somewhere aout an issue with these scopes llocking up or doing something wierd when the "power on cal" reached the offset portion of that procedure.  A firmware update was issued which was supposed to correct the problem.

@PW,

Two ADS1062CA were purchased over 3 years ago.  As far as I know, no firmware update was applied.
The ADS1062CAL was purchased in Dec 2012.  It is still under warranty.
***
If that does indeed add +/-6mv by itself, by the time one adds in the rest of the expression and throws in the DC gain error spec as well, 12-14mv may not be all that far out of spec.
***
What does that really mean?  The Atten Scope may be unreliable when voltage drops to that level?

[picowatt]

@PW,

Two ADS1062CA were purchased over 3 years ago.  As far as I know, no firmware update was applied.
The ADS1062CAL was purchase in Dec 2012.  It is still under warranty.
***
If that does indeed add +/-6mv by itself, by the time one adds in the rest of the expression and throws in the DC gain error spec as well, 12-14mv may not be all that far out of spec.
***
What does that really mean?  The Atten Scope may be unreliable when voltage drops to that level?

Lawrence,

DC measurement accuracy:

±[3%X（|reading|+|offset|）+1% of |offset|+0.2div+2mv]

The above formula from the ADS1000 series manual specifies the accuracy of the scope when performing DC measurements.  I am assuming that the expression [offset] means the distance in volts that the trace is set above or below the center of the graticule.  Let's assume the scope is set to 20mv per division and the trace is offset from the center of the graticule by 20mv (one full division.  Let us also assume the reading at a given point is 6mv.

The first part of the formula is [3%X(reading+offset), or .03X(6mv+20mv) whivh equals .78mv.  To that we are to add 1% of the offset, which is .01X20mv or another .2mv.  At this point we are at +/-.8mv, which is quite reasonable.

However, I am concerned with the manner in which the last expression is written.  If it was written with additional brackets as "+1% of [offset+(0.2div+2mv)]", that last part would only bring the total error up to +/-1.04mv, which would be useable.

However, the way it is written, the expression "+0.2div+2mv" could amount to adding an additional 6mv to the total error, which would make the spec +/-6.78mv, which is pretty bad considering we would be measuring 6mv with an accuracy of +/-6.78mv.  That would mean the measurement could be anywhere in between 12.78mv and -.78mv.  That's pretty bad and also very difficult to believe.

It is very likely that a typo was made when this specification was printed and they did indeed mean to place additional brackets, which would make the DC measurement error of the 6mv in this example +/-1.04mv, that, while not great, is much better than the case where the brackets are eliminated (+/-6.78mv).  It is just a bit strange that they did actually include similar brackets () in the first part of the formula to remove all ambiguity, yet did not do so in the second part.  Also note that in the first part of the expression they use "+/-3%X()" as opposed to the second part that uses "+1%of [offset]+".

It might be worth emailing the factory to see if they did indeed mean to add the additional brackets into the formula.  After looking at it a bit further, this specification would make way more sense if the additional brackets were indeed meant to be there, or at least if they intended the formua to be used as if they were there, so I would not yet "panick" regarding this until receiving further clarification from the factory.     

DC gain accuracy:

≤±3.0%: 5mv/div to 5V/div in Fixed Gain Ranges
≤±4.0%:typical for 2mv/div and Variable Gain Ranges

DC gain error is basically how accurate the volts per division settings are, i.e., when at 20mv per division fixed gain, a division is somewhere between 19.4 and 20.6mv, which is pretty good.

Firmware:

I would get on the factory website and search for "firmware updates" and your model number to see what the latest rev. number is.  Also, there is likely a way to poll your scopes to see what their current firmware versions are (possibly they display that as it boots).  If yours is not the latest version, consider updating the firmware.

As I said, I read somewhere that there was an issue with the automatic "power on" calibration procedure during boot up regarding the offset correcting portion of that procedure.  But, as I recall, it had more to do with the unit hanging up at that point.  Still, the latest firmware is likely advisable.

In your recent shorted probe captures, your offset looked much better than it appeared in previous captures.  You might try an input current measurement with CH2 (the CSR channel) positioned to the center of the graticule as it is in those shorted probe captures and after having pressed the "default settings" button as you said you did (I assume you adjusted Vert sensitivity, etc after you did that).  It is possible you had something set strangely that may have looked like offset.


On that noisey channel, what happens if you turn off the bandwidth limit?  Does it get worse or better?


To check measurement error and offst, as TK suggested, you could use a resistive divider. Solder one end of a 100ohm resistor to one end of a 1 ohm resistor.  Connect the free end of the 100R to the battery plus terminal and the free end of the 1R to the battery minus terminal.  Connect scope probe grounds to battery minus and the probe tips to the junction of the two resistors.  Use !% resistors and a fresh AA battery.  With exactly 1.5V at the battery, the junction of the two resistors should measure 14.8mv.

You can use a DMM to measure across at the resistors' junction as well to double check against what the scope reads.  Use the DMM to measure the battery voltage, the junction of the resistors will measure (Vbatt divided by 101), or 14.8mv with 1.5V at the battery.

PW