spikes caused by the cooling fans

[bjbdts]

Hi, everyone:
I'm using a temperature sensor to monitor the temperature of our sample. The temperature reading is shown in my computer. the sensor is powered up by a 12V regular power adapter. It's working OK until I connect a couple of 12V DC cooling fans to the circuit. They are powered up by the same power adapter as the temperature sensor. I observe there are spikes coming up along with the regular temperature reading. For example, the temperature reads room temperature for a while and then all of a sudden it reads 100degreeC, and then come back to the room temperature. I'm wondering if it's the connection of the cooling fans that causes this problem. The cooling fan has two wires. What's the right way to connect the fans into the circuit?
Thanks,

bjbdts

 

[dpc]

Try a separate power supply for the fans, a much bigger power supply, or some additional capacitors across the 12V. I suspect the motor starting current is causing enough voltage dip in 12V supply that the temp transducer is responding the dip in power supply voltage.

If you have a separate power supply, that would be the best solution. Sensitive instrumentation and motors don't play well together on the same PS.

 

[ScottyUK]

What's the right way to connect the fans into the circuit?

Separate the power supplies. Either use separate regulators from a common input or better still use fully independent supplies. Watch your grounding: avoid the power return path from the fans passing through circuit connections which the analogue circuitry uses. A single ground point is often used to avoid shared paths.


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If we learn from our mistakes I'm getting a great education!

 

[btrueblood]

Depending on the sensor type, you may want to add some shielding over its leads as well, to prevent radiated noise from the motor leads coupling onto the sensor leads.

 

[itsmoked]

Are these pancake fans? Like those found in a PC?

They can put out some noise. Then you hook two up, they will beat together and possibly cause your wall wart's regulator to lose it.

You should, as others have said, use a separate supply.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[OperaHouse]

A couple lines of code could solve that. Average numbers, throw out those that are too high or low. Lets face it, you computer probably isn't doing too much right now. My high school physics teacher taught me order emerges out of chaos. I remember one project where the signal was 85db below the noise and we still got the info we needed.

 

[bjbdts]

Hi,
Thanks for your responses. I first tried to put a capacitor over 12V power supply. The spikes got smaller and appeared less frequently. Then I tried to use a separate 12V power supply. And it worked! The spikes were gone. Really appreciated your helps.

bjbdts