# input impedance...?

Discussion in 'Homework Help' started by KingKK, Feb 13, 2007.

1. ### KingKK Thread Starter New Member

Feb 13, 2007
2
0
hi, i'm a dumb newbie!

I need to find a suitable transceiver for transmitting a voltage signal (0-5 Volts) from a sensor. From the sensor's datasheet I read the following: "Please note connection considerations: Analogue output load is min. 10 kOhm, max. 20 nF."

This means that the sensor has to be connected to a device (load) with an input impedance of at least 10 kOhm, right? But why is the maximum value given in farads?

Thanks

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
That's 20 nanofarads. 2.0^-10 farads. That means that, in addition to the necessary load resistance, you can have problems if the capacitance is too great - like in a long run of coaxial cabling.

What distance do you need to send the signal over, and is it a DC level, or some signal frequency that goes from 0 to 5 volts?

3. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Beenthere,

Doesn't 2.0^-10 end up being the same as 200 picoFarads?

hgmjr

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
All right, 2.0^-8 farads. Having been brought up on micrmicrofarads, nanofarads still give me fits on occasion (saving face here).

5. ### KingKK Thread Starter New Member

Feb 13, 2007
2
0
Oh, that's what it means. Should have guessed it.
Still, thanks a lot.

It's a DC level signal and I only need to send it a few inches (from the sensor to the transmitter). And I'm using two separate wires, so capacitance shouldn't be that big of a problem?

6. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
Won't be enough to measure. I'd twist the wires together to minimize stray noise, though.