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16  Using Arduino / General Electronics / Re: The important of calibration of oscilloscopes. Or not? on: September 02, 2014, 03:29:02 am

I think I understand what you are getting at.

Measurement is either "relative" or "absolute".  

In the engineering world we require measurement to be "absolute" and referenced against "national" standards.

In the domestic world of home electronics, "relative" is generally good enough for practical purposes. viz is this voltage more, equal to, or less than that one.

In the "home brew" system everything is relative and it matters little whether the volt you measure is a "true" volt or not.  

We all own test gear, which no doubt came without "genuine" certification and has never been recertified since the day it was bought.  It matters little as long as it is good enough for the purpose for which it is intended.  And "good enough" is the operative phrase.

I must have the best part of a dozen test meters, a couple of signal generators, a couple of frequency counters and a couple of 'scopes.   None are "calibrated" but they are all "near enough" for practical purposes and for home dabbling that is good enough.   The volt my power supply puts out may not be a "national standard" volt but it is the volt I use and the volt that powers my devices.  

As others have clearly indicated, calibrated test equipment is essential in the industrial environment but that's not the world most of us "play" in. So, if your cheap (or expensive) equipment isn't calibrated but meets your needs, then all well and good.
17  Using Arduino / General Electronics / Re: 240vac Aussie Plug Wiring. on: August 26, 2014, 02:21:06 pm
I agree with John Wasser about principle of a rigid recessed coupling but I would be surprised if that transparent material was anything other than a flexible plastic which effectively negates the intent of a "keyed" insertion device.
18  Using Arduino / General Electronics / Re: 240vac Aussie Plug Wiring. on: August 26, 2014, 03:38:57 am
EU death plugs (no doubt from China). 
Imaging you fail to get them aligned correctly and one pin enters whilst the other passes on the outside of the free socket.
You now have a 50:50 chance that the exposed pin is live
19  Using Arduino / Motors, Mechanics, and Power / Re: How Many amps does this transformer output? on: August 25, 2014, 06:25:04 am
Where does 12 volts and hence 0.625A come from.

The unit clearly states 15 volts at 7.5VA so this equates to a 0.5A output rating on the 15v DC output  (if no current is used on the 17VAC output)
20  Using Arduino / General Electronics / Re: Arduino AC Voltage Dimmer (Variable Resistor? PWM?) on: August 22, 2014, 03:22:02 am
and what do you mean by "65v 60AC"   Do you mean 65volts at 60Hz  and if so where are you getting the 65 volts from (a transformer maybe ?)  Is the lamp frequency sensitive or is it a simple incandescent device.  These are available to operate at such voltages with current draw typically in milliamps. 65 x 0.04 = 2.6watts
21  Using Arduino / Motors, Mechanics, and Power / Re: DC PID motor controller on: August 21, 2014, 05:08:16 am
On the basis that you get one pulse per revolution (measured variable) and that you have a defined period per revolution (set-point) then you "simply" measure the difference (error -  positive or negative) between the set-point and the measured variable and adjust the speed drive signal to eliminate the error.

The PID algorithm contains 3 elements P (proportional), I (Integral) and D (Differential)

If you aren't too bothered about a small degree of fixed error then only the P element is essential.  The controller produces a correction which is proportional to the error - but it never eliminates the error entirely

If you want to eliminate error then use both P and I where the I factor produces a corrective factor dependent upon how long the error exists

The D factor produces a corrective factor based upon the rate at which the measured variable is moving away from or towards the set-point.  For low inertia systems it isn't required.  A typical use would be where a heater is being used to heat up a large mass.
22  Using Arduino / Motors, Mechanics, and Power / Re: DC Motor Current Goes DOWN When Stalling? on: August 21, 2014, 04:57:35 am
I'm afraid harddrive is wrong with his argument.

A centrifugal blower is the pneumatic version of a centrifugal water pump.

The least loaded condition on this type of device is when there is no fluid being pumped - whether it be air or liquid.

Circulatory fluid within the pump body does produce some load but certainly nowhere near the pump's rated capacity.

The stonewall effect that occurs in large centrifugal compressors when the through-flow is restricted, which results in potentially destructive surge, does not apply to "toy" sized pumps such as leaf blowers - the manufacturing clearances are so wide that pump efficiencies are too low to experience such an effect.

When starting large centrifugal liquid pumps the outlet valve must be closed during the run-up phase, then, when the motor is up to full speed the outlet valve is gradually opened.  Suction valves are not used for this process as the loss of inlet head to the pump would induce cavitation resulting in damage to the impeller blades.

Therefore when you blocked your leaf blower, the load flow through the "pump' reduced, resulting in less load on the motor, a corresponding increase in speed and a reduction in motor current.
23  Using Arduino / General Electronics / Re: What is a calabrating battery type called? on: August 18, 2014, 03:52:49 pm
If memory serves me correctly, (it's over 50 years since) we used to use them on Cambridge Pots/bridges  in conjunction with wet ice flasks (cold junction compensation) for the calibration of thermocouple systems.

At that time all our instrument systems were valve operated and, although maybe now considered ancient, were extremely capable of running a nuclear power plant.

Their voltage was somewhere around 1.018 and their output current capability was zero.  Woe betide the apprentice who failed to balance the bridge so that no load was placed on the cell
24  Using Arduino / General Electronics / Re: Safety match activation energy on: August 18, 2014, 02:38:29 am
Don't you think it would make more sense of you got yourself some fine nichrome wire, a box of whatever type of match you are interested in and a variable voltage DC power supply.  With those you could conduct your own empirical tests.  
Using a sledge hammer to crack a walnut (a metaphor for the video shown) doesn't confirm the energy required, it merely demonstrated that enough was used.

As far as maths is concerned Watts is the product of voltage and current   ---   time does not come into the equation
25  Using Arduino / General Electronics / Re: High current Measuring sensor on: August 11, 2014, 01:15:47 pm
Yes I have used hall sensors and in every case they have provided a perfectly adequate measurement system.

The following is extracted from the ASC712 data sheet :

Noise (VNOISE). The product of the linear IC amplifier gain
(mV/G) and the noise floor for the Allegro Hall effect linear IC
(≈1 G). The noise floor is derived from the thermal and shot
noise observed in Hall elements. Dividing the noise (mV) by the
sensitivity (mV/A) provides the smallest current that the device is
able to resolve.

For the subject device with a +/- 20A range the output is specified as 100mV/A with a nominal noise figure of 11mV.
From the above sheet this gives a minimum resolution of 11/100 = 110mA.  With a 20A range, this gives a possible resolution of just over 0.5% referenced to FSD.

For non-scientific applications I would have thought this was more than adequate.

But it's up to each to use what they wish
26  Using Arduino / General Electronics / Re: High current Measuring sensor on: August 11, 2014, 07:19:16 am
Why would you not want to use a hall sensor which provides a simple and reliable method of accurate current measurement and effective electrical isolation with minimum number of components (ie 1)

Erm, because they are much noisier than a shunt or transformer sensor?  Unliklely
to matter for this application.

On what basis do you make that statement.   Transformer unsuitable for DC current sensing so not relevant to the topic
27  Using Arduino / General Electronics / Re: High current Measuring sensor on: August 11, 2014, 02:56:06 am
Why would you not want to use a hall sensor which provides a simple and reliable method of accurate current measurement and effective electrical isolation with minimum number of components (ie 1)
28  Using Arduino / General Electronics / Re: What is a jack plug on: August 02, 2014, 04:05:20 am
The 'male' part is the jack (or plug) the 'female' part is the socket.  (Biology and electronics combined)

If the jack is on the end of a flying lead it is a "free" jack  if it is part of a surface or board mounting it is a "fixed" jack

Similarly if the socket is on a flying lead it is a "free" socket and if it is part of a surface or board mounting it is a "fixed" socket

I once had to explain the difference between male and female threaded components to my secretary - she was rather embarrassed when the penny dropped.
29  Using Arduino / General Electronics / Re: battery mAh tester on: July 31, 2014, 05:46:39 pm
Presume you mean 7000mAH per battery.
Forget the theory and all the fancy gizmos.  If you want to know how long your batteries will last under mains failure conditions then the simplest (and most realistic) test is to turn off the mains and monitor the actual discharge voltage as the batteries supply current to your system.   When voltage has dropped to your predetermined minimum (say 11v) then the time it took to get there is the true application capacity.  OK that takes time, but do you want a truthful answer or an answer that makes you feel good.
30  Using Arduino / General Electronics / Re: LM2575 7.4V to 5V (i don't understand the circuit diagram) on: July 07, 2014, 01:30:11 pm
I recommend you use the charger that came with the phone !!
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