Electronics > Projects, Designs, and Technical Stuff
Advice sought for new Phasor Display
johnkelly1908:
I’m a Lecturer in Electrical Engineering, and I have been looking for many years for an affordable instrument for measuring and displaying phase relationships in AC circuits. I was going to use this instrument in Lab practicals to help students visualise these relationships, and help them gain a more intuitive understanding of the subject. I couldn’t find one, so I made one. I’m bringing it to market, but I realise that this is a very small market.
Would I be better making it an open source development platform for people to make their own instruments? Or is this an overcrowded market?
You can view the instrument here www.actheory.com and I would be grateful for any insights or advice.
dmendesf:
Nice product.
jbb:
This looks like a great product in the works, especially with differential inputs! When I was at university I was amazed how hard some people found the concept of ‘the scope probe is grounded.’
While my natural inclination on seeing it was “what about buttons and a bigger screen,” I think you have a great concept there for educational use; plug it in and it goes. Screen doesn’t need to be giant.
By not doing a battery you’ve saved yourself a ton of irritation (charger, safety, shipping, dead batteries).
Have you managed to get much battle testing in a real teaching lab? That will always find some surprises :)
Some suggestions:
- get some branding on there so visitors to the lab know where to buy their own
- get some labels on the measurement terminals. Especially safety concerns eg what’s the maximum allowed voltage
- you need some technical specs (eg signal levels, input impedance, allowed waveforms, operating and storage temperature range, power supply requirements)
- a spec sheet in printable/emailable format might be critical for getting sales approved
- consider isolating the external power input for safety. If some fool plugs in 415V and blows the guts up, you don’t want the students’ laptop pulled up to line voltage via the USB port. May not be required.
- will performance change if using an isolated USB source like a power bank?
- how’s your input protection?
- lab technicians may be more comfortable if you mention input protection (especially if self-protecting)
- check your power supply will work with crap USB supplies. I suggest trying 4.75V + 0.7 Ohm cable resistance
- check that hot-plugging a USB supply won’t damage the PSU (note you could get quite large spikes on the input due to cable L resonating with input C); 6.0V absolute max chips aren’t reliably up to it here, and a 6V TVS diode won’t reliably clamp below around 9V
rstofer:
The Buy Now button leads me to Amazon.co.uk but that doesn't seem to go anywhere useful. Bummer...
rstofer:
The Analog Discovery 2 does something similar but without the neat phasor display. For the attached plot, I used the Impedance Adapter (because it is handy, it is not required) with the Impedance tool and then selected a 100 Ohm internal (to the adapter) series resistor. Given a 0.1 ufd capacitor, we expect the phase to start out at -90 degrees at 0 Hz and reach -45 degrees when the impedance of the capacitor equals the 100 Ohm resistor and this occurs about 16 kHz, mathematically. Given real-world parts, it occurs somewhere around 18 kHz - close enough.
Note that, for some reason, I didn't start at 0 Hz but 1 kHz. Maybe next time...
The AD2 is cool but the phasor display is much more interesting! Nevertheless, were I an EE student, I would have the AD2 and a few attachments in my backpack at all times.
Sell it or give it away, I don't care which, but I would really like to get one!
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