U4A is just providing a 2.024V Reference to the ADC negative input and to the bottom side of R24. This is not measuring the HAL in any way. It is a unity gain following with input of 1/2 * 4.096V.
U4B is just a unity gain follower with input of:
1.505V + 0.26 * (0 to 4.096V) from Hall sensor or range of 1.505V to 2.57V which is provided to the positive input of the ADC. I have not accounted here for the parallel resistance of what appears to be a fine tune gain control consisting of the 100K pot and two 51K resistors.
In short:
The ADC negative input is being held at 2.024V while the positive input has a range of 1.505 to 2.57V so the ADC output can swing from -0.519V to +5.26V or about 1V swing. The actual swing is a little better than this due to the stuff in parallel with the 10K and C17 is just providing some low pass filtering with cutoff better than RC (10K*100e-9) = 0.1ms Time constant or 10000 rad/s or 1.6Khz cutoff frequency.
To your questions direct:
R24 is providing a bias point for a voltage divider with the input being 2.024V the tap point of the voltage divider is going to the positive input of U4B which measures the HALL Sensor signal. While the hall sensor (it appears) provides a 0 to 4.096V range at most.
R19 is the other side of the divider. You have to use superposition to get the voltage range of U4B from that.
Hope that helps?
Correction slight mistake 1/2 of 4.096 is 2.048 NOT 2.024 my fault!
As far as I can see they are doing 2 different operations.
4B is watching the hall output while 4A is comparing the hall output to 1/2 of the reference voltage.
What is the hall effect type?
Think you may need to provide more info.
If you look carefully 4B is actually a unity gain buffer that has a 2.048V reference input that it is then feeding to the bottom of R24 and the negative input of the ADC.
U4A is just providing a 2.024V Reference to the ADC negative input and to the bottom side of R24. This is not measuring the HAL in any way. It is a unity gain following with input of 1/2 * 4.096V.
U4B is just a unity gain follower with input of:
1.505V + 0.26 * (0 to 4.096V) from Hall sensor or range of 1.505V to 2.57V which is provided to the positive input of the ADC. I have not accounted here for the parallel resistance of what appears to be a fine tune gain control consisting of the 100K pot and two 51K resistors.
In short:
The ADC negative input is being held at 2.024V while the positive input has a range of 1.505 to 2.57V so the ADC output can swing from -0.519V to +5.26V or about 1V swing. The actual swing is a little better than this due to the stuff in parallel with the 10K and C17 is just providing some low pass filtering with cutoff better than RC (10K*100e-9) = 0.1ms Time constant or 10000 rad/s or 1.6Khz cutoff frequency.
To your questions direct:
R24 is providing a bias point for a voltage divider with the input being 2.024V the tap point of the voltage divider is going to the positive input of U4B which measures the HALL Sensor signal. While the hall sensor (it appears) provides a 0 to 4.096V range at most.
R19 is the other side of the divider. You have to use superposition to get the voltage range of U4B from that.
Hope that helps?
In my opinion the circuit could be improved, it is not taking advantage of the entire dynamic range of the ADC.
In my opinion the circuit could be improved, it is not taking advantage of the entire dynamic range of the ADC.
Also, VR2 is allowing you to modify the positive output of U4B from 0 to 5V. But when in the center position is having hardly any effect on the circuit being that the output of U4B has 100 ohms impedance, the VR2 in center makes 50K so it has no effect until it is practically at the end of the potentiometer range.
Hi,
This is part of a gaussmeter circuit. Can someone explain exactly what the resistors R19 to R24 are there for? Also, why are the two op amps places in parallel and connected that way. I believe they are voltage followers, but I don't understand why you need both of them. I
The outputs of the two Op Amps are not really in parallel. Each one having 100 ohms and a 100nF capacitor, the cutoff frequency being 15.9Khz. So no real effect. the one that is in the center C21 is being used to filter VR2. C21 other side could probably have just been routed to ground without much change in circuit behavior.
