I'm going to build some automatic watering system to my garden and i'm wondering that if i use relay to power up water pumps etc, is there way that i can check if device (example pump) works under relay.
It's not enough that i just open or close relay, because if the device under relay is broken, i need to know that somehow.
Since you're not looking for a lot of accuracy and just want fault detection, I'd full-wave rectify the output and just check if it's above whatever threshold would mean the device is working properly.
jremington:
You should also be concerned whether there is water to pump.
A flow or pressure sensor in the output would tell if you the pump is working, and there is water to pump.
That's good idea for water pump. Actually i got one of those from my friend. It calculates some pulses and it would be good for pump. But there will be other electrical devices also, so that's why i asked how to check if device works properly. If it's broken, i guess it won't use any power etc. So no need to any accurate calculation, just to check if it's working or not.
You can also use a flowmeter. This would not only tell you that the pump was running, it would tell you how much water is being applied through that line. It would help keep you from overwatering are underwatering your garden.
pthim:
If it's broken, i guess it won't use any power etc. So no need to any accurate calculation, just to check if it's working or not.
Maybe, but some things can draw excessive current when malfunctioning. A dc motor might use 200mA when operating normally, and use 0mA when off, but use 3A when stalled. You need an upper and lower limit for some things