Protection from voltage spikes

[premkumar9]

Hi,
In a project, to sense water level I used electrical conduction through water as shown in the diagram. These are given to the input of OPAMP LM324. There is a long (abour 15 to 20 meters wire connection between the contact and OPAMP. This has been working well for the last one year. But one problem I faced is that in some cases there was a failure of OPAMP. I guess that it might be due to high voltage spikes (during lightning or so). Could anybody suggest a solution which can be implemented on the existing units?

 

[MrAl]

Hi,

Simplest is to install a cap across the input there, near to the op amp. The cap would go from input to ground before the input resistor of the op amp.
Depending on the speed of response needed, you can use a 0.1uf cap up to 10uf and that should do it.