Troubleshooting Inductive Sensor

[braddo_99]

So dlloyd, you're suggesting to put the fan and the sensor and the 4k7+LED all in parallel? That will be fine for the sensor, and will get me the low from the output I'm looking for, but will cause my fan to blow more than desired, but I guess I could also put a resistor in front of it as well? Adding a resistor to the fan though would I guess heat it up and waste some power.

[dlloyd]

So dlloyd, you're suggesting to put the fan and the sensor and the 4k7+LED all in parallel? That will be fine for the sensor, and will get me the low from the output I'm looking for, but will cause my fan to blow more than desired, but I guess I could also put a resistor in front of it as well?

It will have no effect on the fan as it's connected across the 24V DC power source. It will provide about 4.7mA through the LED (using I=V/R, I=(24-2)/4700 = 4.7mA). You have  +24 •---4.7K---•---►|---• (-)

[braddo_99]

The fan was not previously connected across 24v - it was connected in parallel with the sensor but in series with the LED, so the fan was only seeing 10v.

[braddo_99]

Did my replay of your suggested zener configuration make sense with respect to how it would work with the trigger low board sensor?

[dlloyd]

The fan was not previously connected across 24v - it was connected in parallel with the sensor but in series with the LED, so the fan was only seeing 10v.

It would be really good to know the purpose of the LED and fan.

... I want the LED and fan to both always be on, no change when sensor triggers or not ...

From this, It seems the purpose of the LED is a power indicator for the 24V supply.

For the fan, it seems it's for basic cooling, always running as long as 24V DC power is available.
If the fan is only rated for +12V, you'll need a resistor connected in series with it. With a multimeter, you could measure the resistance across the fan, then use something very close to this for the series connected resistor value. The minimum power rating of the resistor would be I²R or V²/R where V =12V.

Did my replay of your suggested zener configuration make sense with respect to how it would work with the trigger low board sensor?

See reply#12 by Runaway Pancake

[runaway_pancake]

braddo,

In both of your sensor's states, sensing and not sensing, V_in is greater than V_z, so you will (given "case A") always have V_z, as you gather.

The zener output never "goes to ground" (in some catastrophic failure that might happen).
In "case A", the zener conducts when V_in is greater than V_z.
When V_in is less than V_z then the zener is not conducting.

If you use "case B" with a 20V zener, the output would be 4V with 24V V_in and "0" with anything else.

You could check that out by doing an experiment with your 5V zener where the two states should be be 19V (24 - 5) and 9V (14 - 5).
Careful of your zener current.
(I haven't been noting your values and so on, been keeping things conceptual - the heavy lifting I leave to you.)

[braddo_99]

dlloyd, yes, the fan is for general cooling and the led is for general lighting, not necessarily a power indicator, although it will certainly indicate that.

Pancake, so my two questions are still not quite clear - in "case A" when the zener is in its conducting state, will the board sensor "see" ground and hence be triggered?

Then, since the ground is floating on the sensor and since I'm getting this 24v unsensed, 14v sensed thing, neither config of 5v zener will do the job. I hadn't thought of a 24v > zener > 14v option... don't have one of those, really did think some divider would get the job done but still a mystery.

Simplest seems to make all in parallel and load them down with resistors to get the amount of air/light needed.

[dlloyd]

Another idea for you're experiments ... use a regular diode instead of a zener:

[Paul__B]

Do not put the fan and LED strip in series.  OK?  It will likely cause trouble and none of us can help you if you intend to do that.

Well, I suppose if it happens do what you want, it is up to you.  More important is that the sensor is not compromised by being connected in any way other than directly to its correct supply.

If you need 12V with any accuracy and you only have a 24V supply, you use a regulator to drop the voltage - a 7812.  Not a Zener.  If the 24V is regulated and the load is constant such as the LED, a series resistor will do.  If you need to slow a 24V fan, you can try running it with a 12V regulator or if that is too slow, just put a resistor in series with (only) the fan.  You have to work out what current the fan draws and what power rating the resistor needs to be.

dlloyd has it seems given you the best solution for the sensor.