First off, see the attached pic for the piece of machinery i'm referring to.
Hi all,
I'm hoping that someone could provide me with advice about how to implement a vacuum loss alarm.
My father, who's an agricultural contractor, has a large seed drill that has no alarm function to show when it's looses vacuum pressure under the hopper. This is usually caused by running out of seed or the drive belts failing, both of which are hard to realise from the cab as most of the operator's concentration is spent on making sure they keep the machine on it's designated tramline.
The bit i'm having trouble with is trying to work out what kind of air pressure sensor I should use - i.e. gauge pressure sensor or differential pressure sensor. Could anyone also point me in the direction of a sensor that would do the job. I'm less concerned with the strength of the vacuum, and more with how close to atmospheric pressure the chute under the hopper is.
Thank you in advance.
if you have a differential sensor that can do 1 Atm (=1013 hPa) that should do the trick.
However how vacuum is the vacuum under the device?
How much variation is considered loss of vacuum?
for how long time?
how many steps - accuracy / precision?
Think you have to quantify the problem first before you can select the right sensor
- Given it is on a agri-device it should also be almost "mil spec" robust I assume .
- measuring vacuum cannot be done with simple rubber hoses)
This seems like the sort of thing that would be best implemented using a vacuum switch. You could use that to operate a sounder or warning lamp directly - no electronics or microcontroller required.
robtillaart:
if you have a differential sensor that can do 1 Atm (=1013 hPa) that should do the trick.
However how vacuum is the vacuum under the device?
How much variation is considered loss of vacuum?
for how long time?
how many steps - accuracy / precision?
Think you have to quantify the problem first before you can select the right sensor
- Given it is on a agri-device it should also be almost "mil spec" robust I assume .
- measuring vacuum cannot be done with simple rubber hoses)
The exact strength of the vacuum varies as the vacuum pump is driven by the PTO shaft from the tractor which varies significantly with engine RPM, hydraulic system load, and various other factors.
I'm defining loss of vacuum as being near to atmospheric pressure, because I don't know whether the chamber will maintain a slightly lower pressure than atmo if the pump stops. My idea to overcome this was to calculate a metric by comparing the drill's pressure to atmo pressure and activate the alarm if the value drops below a certain value. This way, if false alarms are being generated, I was going to have two switches connected to the Arduino that either increase or decrease the value so the operator can calibrate to the most appropriate value themselves.
As for duration, pretty much a couple of seconds, taking into account any false readings that may arise (not sure there). Responsiveness is the name of the game here, otherwise when the crops start to grow you wind up with ugly misses all across the fields as you sometimes see where less... experienced operators have been.
I was going to have the sensor assembly housed inside an ABS IP65 enclosure I have.
