I have similar project where I am trying to detect if a pump has stop or is in motion.
I am running a pneumatic pump which operate from 0.5 to 250 HZ. The sensor feedback is NPN proximity switch.
One of the problem I had is that when the pump stops, it can stop on the prox-switch and give a high (+Vd) or NOT on the prox-switch which gives a low signal (0V grounded).
I seemed to solve this problem by using two 555 timers in parallel ( inverted one of the 555 input), then ANDing the outputs of the timers. This will give me High output if only if both timers outputs are high. This solves the problem if the pump is stopped on the with it on or off the prox-switch.
This is basically two of the missing-pulse detector parallel then "Anding" the output of two 555's (one 556), the trouble starts at the pulse width threshold, this is the at low speed operation (~<1hz). When the input pulses are below the 1-2 hz, the output of the AND gate will oscillate when it drops below the threshold frequency.
The output will be use to signal a computer that the pump is running. Their are some off the shelf frequency counters that have alarm outputs but are in the $300-500 range.
I'll have to interface this with a 24VDC control circuit, so I'll have to use a regulator to get it down to 15VDC. It draws about 40-50ma. I would like to fit this in a 22mm x 22mm x 50mm space.
Anyone have a suggestions for a simpler circuit.
I am running a pneumatic pump which operate from 0.5 to 250 HZ. The sensor feedback is NPN proximity switch.
One of the problem I had is that when the pump stops, it can stop on the prox-switch and give a high (+Vd) or NOT on the prox-switch which gives a low signal (0V grounded).
I seemed to solve this problem by using two 555 timers in parallel ( inverted one of the 555 input), then ANDing the outputs of the timers. This will give me High output if only if both timers outputs are high. This solves the problem if the pump is stopped on the with it on or off the prox-switch.
This is basically two of the missing-pulse detector parallel then "Anding" the output of two 555's (one 556), the trouble starts at the pulse width threshold, this is the at low speed operation (~<1hz). When the input pulses are below the 1-2 hz, the output of the AND gate will oscillate when it drops below the threshold frequency.
The output will be use to signal a computer that the pump is running. Their are some off the shelf frequency counters that have alarm outputs but are in the $300-500 range.
I'll have to interface this with a 24VDC control circuit, so I'll have to use a regulator to get it down to 15VDC. It draws about 40-50ma. I would like to fit this in a 22mm x 22mm x 50mm space.
Anyone have a suggestions for a simpler circuit.
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