Output signal of a NPN limit switch

Status
Not open for further replies.
J

jungle

Newbie level 4
Joined
May 10, 2016
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
69
Hi everyone,
I am using this limit switch (LS): D-F9N (NPN - sink) output. I used an oscilloscope to monitor its output. The observed output is under two cases as follows:
1. Zero volt DC if the LED of the LS on.
2. A noising signal around zero if the LED off.
Is it a normal working condition for LSs? (The LS is powered at 24VDC)
Please give me some suggestions.
Thank you.
 

Hi,

I don't know what a D-F9N switch is....

But any low side switch can (as it name says) only switch to GND (=LOW).
If not switched LOW, then it is open = high impedance, this causes a floating node.

The voltage of a floating node is undefined. It may be DC of any value, AC of any value or any random waveform.

It's like a piece of wire in your hand.

A voltmeter is no useful device to "measure" the high impedance state. An ohm-meter is more useful.

Klaus
 
Reactions: jungle

    J

    jungle

    Points: 2
    Helpful Answer Positive Rating
A NPN switch has no useful output signal without the pull-up resistor of the connected load, e.g. PLC "NPN" input.
 
Reactions: jungle

    J

    jungle

    Points: 2
    Helpful Answer Positive Rating
Thanks for the useful reply!

One more question, should I connect to a pullup- resistor (If yes, how can I calculate resistor value?) or just directly connect is okay?
 

jungle said:
Thanks for the useful reply!

One more question, should I connect to a pullup- resistor (If yes, how can I calculate resistor value?) or just directly connect is okay?
Click to expand...

A direct connection to 24V would burn out the transistor switch.

Normal use is 10mA or 2.2k to 2.4k in series to 24V if desired. with < 0.8V when the NPN conducts.

 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…