OPamp problem with students

[barrybear]

I have built some simple opamp occilator boxes for students to take readings from.
Square ,sine and triangle waves are generated with voltage outputs from200mv to 5 volts. frequencys from 40 hz to 20khz. they plug 20 volts dc in and an ossiloscope to the output all connections are with 4 mm plugs 2 for dc volts in and 2 for output to scope .
The problem is that often they plug the power in to the output connections and blow the opamp up .
Has anybody got any idea for an opamp that could take a little abuse .the chip that always blows is the AD 820AN single package opamp.

Thanks for any help

 

[Old Nick]

why not just make the output of the box a BNC type or similar, so that your students can't plug the power into the o/p. BNC should connect straight to your scope with a cable (save getting your scope probes broken aswell.

 

[barrybear]

I did talk to my head of department about this but he was insistant that all connections to the box would be 4 mm plugs as that is the standard connection within the physics department. (school scopes to and they are 4 mm as well).

 

[Siniša]

Input of scope is 1MΩ. Just put 5-10kΩ resistor in series with oscillator output. This is simplest, but it works only for high impedance load.

Also you could have relay that connects output of opamp only if they plug in power properly. This is usefull if they hook various loads to it to see what happens. It does not prevent ocassional moron to try what happens if power supply is connected on both ports. Idiot proof is oxymoron.

Third solution is buy large stock of opamps. This solution gives you job security which is hard to find these days.