LED to light when load detected?

[NewUser]

I plan to build a small battery-powered (2x9V) tester to test the operation/alignment of 24vdc industrial sensors while showing whether the output is pnp or npn, using the 18v supply to power the sensor.

I'd like to add an LED to prove that the sensor's supply is hooked up while in its unswitched and output-unconnected state. Is there a simple method to light an LED when a current draw is sensed? (most of the sensors probably draw a few mA in their unswitched state). As I don't plan to have an on/off switch it would also be spiffy if the current draw, with sensor unconnected, is teensy.

BTW, RS Components sells this gadget for around US$100!

 

[ericgibbs]

I plan to build a small battery-powered (2x9V) tester to test the operation/alignment of 24vdc industrial sensors while showing whether the output is pnp or npn, using the 18v supply to power the sensor.

hi,
Can you explain what you mean by output is pnp or npn.

Do you mean a negative voltage or positive voltage swing?

 

[NewUser]

hi,
Can you explain what you mean by output is pnp or npn.

Do you mean a negative voltage or positive voltage swing?

When one buys a 3-wire industrial sensor, say a proximity switch, you specify both the voltage, usually 24vdc, and its output, PNP or NPN; ie PNP = a positive output on a "detection" (for a "normally open" switch), and vice-versa.

Here is something similar to what RS offers for extortinate prices:
**broken link removed**

 

[NewUser]

And from that link:

"If the tester is improperly connected to a sensor, a safety feature prevents damage to either to tester or the sensor. "

I wonder if that's simply a 5c diode

 

[ericgibbs]

And from that link:

"If the tester is improperly connected to a sensor, a safety feature prevents damage to either to tester or the sensor. "

I wonder if that's simply a 5c diode

Downloaded your datasheet link, will look thru later.

Are located in UK?

 

[NewUser]

Are located in UK?

Close. One of H.M's subjugated, ie Down-Under