Hey everyone!
I'm an undergraduate in a physics lab, and I have been charged with making a fail-safe system for one of the experiments. I'm having some troubles, and wondered if you guys could help out.
As part of my system I have built a circuit (schematic attached) that when it receives a signal it shuts off another part of the experiment. I am monitoring 6 different parts of the experiment, and I have split those parts into two sections on the circuit. One section receives signals from 3 flow switches, and the other receives signals from a flow switch and the comparator. When the flow switch or comparator leaves the defined range my circuit should send a signal to shut off different parts of the experiment and not allow them to turn on. This is done by recieveing a signal through an OR gate, and sending the output of the OR gate to an RS flip-flop. The flip-flop is then connected to some relays that control different parts of the experiment. The circuit that I have built functions how I want it to. However it seems to have be very sensitive to ESD and transient changes in the ground. That is, whenever there is an ESD near or on the box containing it the flip-flop gets triggered and changes state. Also, when an electronic device is plugged into a receptacle in the wall (near to where my power supply is plugged in) the flip-flop gets triggered and changes state. I think this is due to a voltage spike at the input at the OR gate (which are all grounded when not receiving a signal).
A few notes:
1. I've made sure that everything is grounded through the ground coming through my power supply, including all of the unused inputs to the OR Gate.
2. I've checked one of the inputs at one of the OR gates with an oscilloscope, and there is a very transient voltage increase (or decrease) when I plug or on unplug something into a receptacle (****The device must be on before being plugged in to consistently repeat this phenomena. This is probably not good practice, but I need to make my circuit so that it isn't sensitive to this*****). I think this may be the cause of my problems. However, I don't know how to fix this issue.
3. I've considered adding an inductor through my ground to try to suppress the voltage spikes. However, I think I would need a very large inductor, which would be impractical (maybe).
4. A friend suggested I look into using an opt-isolator. I've done some reading on this, but I'm not sure where I would implement it.
I'm VERY new to electronics and am probably violating a ton of rules. With that said, I would love constructive criticism on the circuit and some suggested solutions to my issue.
Thanks in advance!
Thenobsta
I'm an undergraduate in a physics lab, and I have been charged with making a fail-safe system for one of the experiments. I'm having some troubles, and wondered if you guys could help out.
As part of my system I have built a circuit (schematic attached) that when it receives a signal it shuts off another part of the experiment. I am monitoring 6 different parts of the experiment, and I have split those parts into two sections on the circuit. One section receives signals from 3 flow switches, and the other receives signals from a flow switch and the comparator. When the flow switch or comparator leaves the defined range my circuit should send a signal to shut off different parts of the experiment and not allow them to turn on. This is done by recieveing a signal through an OR gate, and sending the output of the OR gate to an RS flip-flop. The flip-flop is then connected to some relays that control different parts of the experiment. The circuit that I have built functions how I want it to. However it seems to have be very sensitive to ESD and transient changes in the ground. That is, whenever there is an ESD near or on the box containing it the flip-flop gets triggered and changes state. Also, when an electronic device is plugged into a receptacle in the wall (near to where my power supply is plugged in) the flip-flop gets triggered and changes state. I think this is due to a voltage spike at the input at the OR gate (which are all grounded when not receiving a signal).
A few notes:
1. I've made sure that everything is grounded through the ground coming through my power supply, including all of the unused inputs to the OR Gate.
2. I've checked one of the inputs at one of the OR gates with an oscilloscope, and there is a very transient voltage increase (or decrease) when I plug or on unplug something into a receptacle (****The device must be on before being plugged in to consistently repeat this phenomena. This is probably not good practice, but I need to make my circuit so that it isn't sensitive to this*****). I think this may be the cause of my problems. However, I don't know how to fix this issue.
3. I've considered adding an inductor through my ground to try to suppress the voltage spikes. However, I think I would need a very large inductor, which would be impractical (maybe).
4. A friend suggested I look into using an opt-isolator. I've done some reading on this, but I'm not sure where I would implement it.
I'm VERY new to electronics and am probably violating a ton of rules. With that said, I would love constructive criticism on the circuit and some suggested solutions to my issue.
Thanks in advance!
Thenobsta
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