exact current and potential source
in [Basics]
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From: Kari Laine on 23 Apr 2010 13:51 Hi, I am testing several things and now I would need a very exact current and voltage source. It would be nice if it were correct to 0.001mV/mA. Even more is better but I think that pushing a little. I can't probably construct one myself from a schematic. So ready devices preferred. If the prices are high then that mentioned self building might be option... Best Regards Kari -- PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI - KEYPADS - ACCESSORIES http://www.byvac.com (I am just a satisfied customer)
From: Kari Laine on 24 Apr 2010 04:08 whit3rd wrote: > On Apr 23, 10:51 am, Kari Laine <klai...(a)gmail.com> wrote: > >> I am testing several things and now I would need a >> very exact current and voltage source. >> It would be nice if it were correct to 0.001mV/mA. > > One can purchase pre-trimmed reference voltage components, > like AD581, with various precisions ($5 to $40). Standard cells > (with a calibration certificate) are higher. > > Nothing will get you to .001 mV unless your laboratory setup > includes VERY tight temperature controls; wiring thermocouple > effects make anything below .05 mV into a difficult exercise. Sorry I made a mistake. I meant .001A and .001V not mA/mV so.... I will google for the AD581. > > A calibrated voltage source, an attenuator (some of the old > potentiometers, available on the internet at bargain prices, will > hold four-digits of accuracy easily) and a few precision resistors > makes it possible to generate lots of voltages and currents > with simple operational amplifier circuits. Alas, you DO have > to know and treat all the important error sources to do this kind > of precision work. > > Voltmeters in parallel have the same applied V; ammeters in serial > have the same applied I. Everything else, you gotta keep track of > errors and error propogation. I need it for calibrating the oscilloscope. I don't have another source for calibration. I am writing an oscilloscope program to Velleman PCSGU250. It is at it's early stages - ALPHA! But can be had from http://www.lnxcore.net If you don't have the hardware connected it starts in a mode where you can play with sin waves and select X-Y Plot from menu. Basic principle to me is that I will make possible to simulate scope without hardware and therefore develop the program. Velleman is at http://velleman.be The frequency analyzer and bode plotter has proven to be very difficult to me. NOTE ! http://www.syscompdesign.com/ makes and Open Source version of oscilloscope, which works with Windows, Linux and MacIntosh. I am now going to spend 1-2 weeks to add support for Velleman PCSGU250 to it. Best Regards Kari -- PIC - ARM - DISPLAYS - RELAYS - MODULES - CONVERTERS - I2C - SPI - KEYPADS - ACCESSORIES http://www.byvac.com (I am just a satisfied customer)
From: John Fields on 24 Apr 2010 14:09 On Fri, 23 Apr 2010 20:51:53 +0300, Kari Laine <klaine8(a)gmail.com> wrote: >Hi, > >I am testing several things and now I would need a >very exact current and voltage source. >It would be nice if it were correct to 0.001mV/mA. >Even more is better but I think that pushing a little. > >I can't probably construct one myself from a schematic. >So ready devices preferred. If the prices are high >then that mentioned self building might be option... --- What you're looking for is called a "current shunt" and is essentially a low resistance precision resistor which is wired in series with the load and the voltage dropped across it [the shunt] measured in order to determine the current through it. In order to comply with your spec, what you need is a shunt with a sensitivity of 1 millivolt per ampere, which is readily available and is called a "100 millivolt shunt" in the trade. That 100 millivolts refers to the voltage which will be dropped across it with 100 amperes through it, and an example would be at: http://www.deltecco.com/MKA-DC.html Unfortunately, there's an error in their literature which specifies that an ammeter is used in conjunction with the shunt in order to measure current, when what they mean is 'voltmeter'. JF
From: John Fields on 24 Apr 2010 19:47 On Sat, 24 Apr 2010 13:09:24 -0500, John Fields <jfields(a)austininstruments.com> wrote: >On Fri, 23 Apr 2010 20:51:53 +0300, Kari Laine <klaine8(a)gmail.com> >wrote: > >>Hi, >> >>I am testing several things and now I would need a >>very exact current and voltage source. >>It would be nice if it were correct to 0.001mV/mA. >>Even more is better but I think that pushing a little. >> >>I can't probably construct one myself from a schematic. >>So ready devices preferred. If the prices are high >>then that mentioned self building might be option... > >--- >What you're looking for is called a "current shunt" and is essentially a >low resistance precision resistor which is wired in series with the load >and the voltage dropped across it [the shunt] measured in order to >determine the current through it. > >In order to comply with your spec, what you need is a shunt with a >sensitivity of 1 millivolt per ampere, which is readily available and is >called a "100 millivolt shunt" in the trade. > >That 100 millivolts refers to the voltage which will be dropped across >it with 100 amperes through it, and an example would be at: > >http://www.deltecco.com/MKA-DC.html > >Unfortunately, there's an error in their literature which specifies that >an ammeter is used in conjunction with the shunt in order to measure >current, when what they mean is 'voltmeter'. --- Equally unfortunately, there's also an error in my description, since a 100 millivolt shunt is a shunt that's made to drop 100mV with a _specified_ current through it, not just 100A. For example, the Delteco MKA-100-100 is a 100A 100mV shunt, while the Delteco MKA-10-100 is a 10A 100mV shunt. JF
From: John Fields on 25 Apr 2010 11:45
On Fri, 23 Apr 2010 20:51:53 +0300, Kari Laine <klaine8(a)gmail.com> wrote: >Hi, > >I am testing several things and now I would need a >very exact current and voltage source. >It would be nice if it were correct to 0.001mV/mA. >Even more is better but I think that pushing a little. > >I can't probably construct one myself from a schematic. >So ready devices preferred. If the prices are high >then that mentioned self building might be option... --- I misread your requirements, please disregard my earlier posts. JF |