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15 Threads found on Megohm
you can buy these two silicon chip magazine article online about such meters there is a detailed description of how it
The most important differences between both circuits are * the gain (opamp: 1E5...1E6; diff. stage: 10...100), and * the output impedance (opamp: 50...100 ohms; diff.stage: kohm range). * input impedance (opamp: megohm range; diff. stage: kOhm range) (The differential output of the diff. stage would not create any problems; there are operati
I have found this effect many years ago. the problem is that any spikes or noise on the mains gets through the diodes and pumps up the capacitor. With a 10 megohm DVM, there is no load on the capacitor so the peak voltage is indicated, however if it this effect a small load, say a 10K resistor wired in should stop this effect. FYI the circuit where
NE5532 is very good for most audio applications but it's input bias current may be to high for your equalizer circuit because the bias resistors are very high value (1 megohm). OP noise current will be even more problematic for an audio application. Every OP type has an optimal noise matched source impedance. For NE5532 it's in a
This says that 1X scope probes have a resistance of 1 megohm.....i thought it was zero Ohms? ..if you please, scroll down to where it is titled "oscilloscope probes"
If you use a circuit such as the one above, put a pair of back to back diodes from your input to earth to protect the amp from overloads. If you use a 10 megohm probe that was designed for some other scope, use it and wire a 50pF trimmer from + i/p to earth in your amp. This should then be adjusted to get the best response from prob+amp. As the out
If you measure V1 with a DVM, this will have a 10 megohm input impedance so the extra current, will be very low, and as you know its a 10 megohm resistor you can compensate for it in your calculations. Frank
My key fob uses a single lithium coin cell. I question the use of starting with such a high primary voltage, especially if you insist on using linear regulators. One approach might be to use a crude very low current regulation, such as a diode stack (or low current zener) and a megohm resistor for "sleep mode", and have the uC's first task be to
I think you can use an audio millivoltmeter; some do respond to 40 kHz. Or, you can use a simple diode detector with a DVM or an analog milliammeter. You can calibrate it on your good receiving transducer; then it should work with other transducers, too. An oscilloscope typically has ~ 1 megohm input impedance; other devices like I suggested m
Begin by looking at the feedback pin voltage. If that's in spec (bearing in mind that megohm meter input impedance could bend the answer by over 10%, given the values you used) then it's an external tolerance problem, a ground offset, or something. At that high an impedance things like ESD protection leakage, input bias currents (if non-
Those resistor values seems a bit high... 1 megohm in bias for a bipolar transistor?? and 20 kohm in collector... I would try to run a tad higher Icq, but maybe you did shoot for ultra low current??
Low currents can be measured with an electrometer amplifier and a high megohm feedback resistor. Typical feedback resistors are in the range 100 to 1000 MΩ. This is often used for measuring the small currents produced in ionization chambers, etc. The electrometer amplifier summing junction can't be connected directly to the circuit board
If carefully constructed, a series resistor into 50 ohms makes an excellent wide-bandwidth low-capacitance probe - much better than typical 10X 10-megohm passive probes. However, the resistance probe will load your circuit somewhat, but that's usually not too important when probing RF and high-speed logic. You must decide if the load will affect yo
There is also the saturation problem. Put a diode between pins 1 and 2 so that the output can not go lower than 0.6 V below the input. This will keep the op amp out of saturation and help the speed problem. Can you have a negative voltage supply for the amplifier? On the input use a diode in series (not shunt) and a megohm resistor from the
In general, the spice matrix solution does't like high impedance nodes with no path to ground. For instance, two capacitors in series may not converge. I don't know how the component is made in hspice but you might try large resistors (multi megohm) to ground at the point where the transmission lines connect together. That should not affect your