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Most accurate signal generator
BennoG:
Or even better use a scope, then you can see what you are measuring.
There are cheap scopes that even will go to 1Mhz.
Personally I use usb based scopes (Picotech) but everyone has his / her own preferences for scopes.
Benno
shapirus:
--- Quote from: BennoG on March 26, 2024, 01:16:39 pm ---Or even better use a scope, then you can see what you are measuring.
--- End quote ---
But even the not so cheap ones can hardly meet the required measurement accuracy. Frequency yes definitely, even cheap scopes are quite good at that, but amplitude not so much.
It may make sense to build a relatively simple bipolar peak detection circuit that will allow to measure positive and negative amplitude peaks and fine tune the generator's output to the desired AC level and remove the DC offset.
Can also be done, reasonably well at this frequency, using a simple ADC like MCP3304 (but then again you'll need a suitable DMM to calibrate it).
nctnico:
--- Quote from: loop123 on March 26, 2024, 01:03:08 pm ---
--- Quote from: BennoG on March 26, 2024, 08:21:30 am ---The OP probably does not understand that the output load needs to be 50 ohm. If you not load the generator with 50 ohm the output voltage is usually double the output voltage you set on the generator.
Or for the el cheapo chinese the unloaded output is the set voltage and as soon as you put a load on the output the voltage drops.
Benno
--- End quote ---
The E1DA ADC has input impedance of 640 Ohm while the Scaler has input impedance of 200k Ohm. What would happen to the signal generator with 50 ohm output impedance in them?
--- End quote ---
With the generator set to High-Z mode (which is just an amplitude reading scale factor), you'll need to adjust the amplitude reading by a factor from the resistie divider of 50 / 640 Ohm or 50 / 200k Ohm. Another option is to put the generator in 50 Ohm mode and put a resistor parallel with the load to make the load resistance equal to 50 Ohm.
Using High-Z mode is likely the most accurate because the deviation of the internal resistance influences the result the least. With Low-Z mode you have to assume the output resistance of a cheap generator is actually 50 Ohm. A difference of a few Ohm makes a large error.
Fungus:
--- Quote from: loop123 on March 26, 2024, 06:48:42 am ---No. I just wrote 1.00001V to drive the point that it should not be 1.2V or 0.9V but exactly 1V. It doesn't have to be 1.00001V but only 1.01 volt for example. It is enough.
--- End quote ---
--- Quote from: loop123 on March 26, 2024, 01:03:08 pm ---My multimeter has this specs up to 500Hz only. What best inexpensive multimeter that can measure at least 10Hz to 20000Hz with accuracy of 1/100000th (ops, i mean just accurate enough in 2.01V or 3000.01 Hz?
--- End quote ---
Beware: Multimeter bandwidth ratings are dubious at best. I wouldn't use one with less than "100kHz" rating to measure a 20kHz signal.
I wouldn't use a multimeter at all for this, not when you can get a good-enough oscilloscope for $30.
https://www.aliexpress.com/item/1005004986731615.html
(get the 18MHz version with the proper oscilloscope probe, not just the crocodile clips...)
Verify the oscilloscope's voltage accuracy by measuring a fixed DC voltage (not an AC signal) and comparing with your multimeter. I'm sure it'll be close enough for your needs though (I own two of those 'scopes).
Anthocyanina:
for your original 200$ budget, i would get an owon HDS242S. it's a very reasonable oscilloscope, multimeter and generator for the price, here's the owon's generator in yellow, vs a keysight 33212a in blue, both set for the same frequency and amplitude of 1.8vpp. you can see the measured Vpp and frequency for both channels to the right of the waveforms.
keep in mind that the output of both generators is going to a high impedance load (the analog discovery's 1Mohm inputs) and will be halved if you connect them to a 50 ohm load. the owon can output 5vpp to high impedance loads and 2.5vpp to 50 ohm loads, so if that doesn't work for you, then yeah, this won't work, but within that voltage range, the generator of the owon is pretty reasonable for the frequency range you want, and you also get an oscilloscope and multimeter.
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