Joerg, are you saying, the function (ramp, sawtooth ect,) will be so slow and linear to be a good aproxamation of time?
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19 years ago
Joerg, are you saying, the function (ramp, sawtooth ect,) will be so slow and linear to be a good aproxamation of time?
Good elecs have discharge tau's in days.
So turn the pot.
The op "knows some basics" and wants a chart recorder to sweep. So you're suggesting he learn to program a PIC and lay out a board with DACs and stuff?
The RC thing is something anybody can make in a few minutes from a few RatShack parts, and once it's running it will be easy and obvious how to tweak it.
John
The linearity of a charging cap depends on how close to the battery voltage you allow it to go; the higher the cap voltage goes, the lower the slope and the worse the curvature. If you use a 9-volt battery to charge a cap through a resistor, and only use the first volt of the resulting voltage ramp (namely set your chart recorder to sweep over the 0 to 1 volt range), the ramp error will be roughly 5%; to be exact, the slope at the and of the 1-volt ramp is 11% down from the slope at the start.
If you use 0.1 volts of a potentially 9 volt ramp, the linearity error is below 1%.
Try it!
John
Thanks , I looked for one like that, and it was on sale for $53,000. I will fool with the RC and see what happens.
pot----------*--------*---------to recorder+
*-----------------------------------------*--------*--------- recorder -Yeah, good idea, he did say he had MV input ranges, good reduction!
Rocky
Okay, here's a sketch, but I do NOT have time to support it, sorry. Ignore any shwarma or mango stains.
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Hello,
Yes. For example, the Wavetek function generator in our lab is digitally controlled and operates from 10mHz (milli-Hertz) to 12MHz. So this one can do a 100-second ramp. Not quite long enough for your application but I am sure you could find one that goes below 1mHz. It can do ramp-up, ramp-down, triangle, sine and all kind of other tricks. Great linearity. Everything is programmable, including output amplitude and offset which is importannt with x-y recorders. Most of them also display and store the programmed values so it'll be the same when you turn it on the next morning.
But it must be a digitally controlled version, not some cheap RC solution. So look around for one with a digital readout (LED or LCD).
Regards, Joerg
I read in sci.electronics.design that " snipped-for-privacy@sover.net" wrote (in ) about 'ramp time to voltage', on Fri, 29 Apr 2005:
No, both charge and discharge are exponential.
It's rather simple to charge (or discharge) your cap though a constant-current source, which gives a linear ramp. You can even buy one, looking like a transistor. But you can also make one with two transistors and two diodes or an LED. I don't have time to draw you a diagram at present, sorry.
-- Regards, John Woodgate, OOO - Own Opinions Only. There are two sides to every question, except 'What is a Moebius strip?' http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Hello,
No idea where that price came from. Refurbs are often around $1000, on Ebay they can go for a few hundred, with some luck under $100. Here is one that supposedly goes down to 100 Mikrohertz, but you'd have to check that and whether it does what you want:
These are often found cheaply on Ebay.
Regards, Joerg
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