RF Frequency effect on Inductive proximity 1

[rauthr80]

Hi

In one of my application I am using Inductive Proximity sensor along with spped monitor to control speed of motor. But Sensor is getting affacted by RF frequency used by wakytalky. Can you sugest any method to eliminate RF frequency effect.

 

[VEBill]

Probably in this order:

Shield the cabling (you can often obtain suitable braid from large coaxial cable).

Add ferrite snap-on cores. It's best to confirm the frequency range of the core material to make sure it maches the walkie-talkie's frequency.

Add bypass capacitors, but you'll have to check many aspects of the design to choose capcitors that won't affect the circuit.

Put up a sign - 'No Walkie-Talkies'.

 

[Comcokid]

Most likely the cable is picking up the RF and a junction on the sensor output is rectifing the rf signal. Try shielded cable and a bypass capacitor - use about 100 to 500 pf for a wakytalky less than 100 MHz, or a 15 to 30 pF for higher frequency wakytalky - with as short a lead length on the capacitor as possible.

 

[VEBill]

"...as short a lead length on the capacitor as possible..."

There's a trick that actually takes advantage of the bypass capacitor's lead length. You choose the lead length to series resonate at the frequency band that you wish to bypass. Alternately, you select the bypass capacitor's value such that it series resonates at your chosen band given the actual lead length when installed.

One of the ARRL handbooks has further information (tables and/or charts).

This is not a necessary technique, but if the bypass capacitor's leads must be long, then you might as well take advantage of the fact rather than fighting it.

For the original poster, in his case it is likely common-mode pick-up and any bypassing would (first) be from the wires to ground, then (second) across the signal if you get to that point.

But due to the effort, bypass capacitors would be the (hopefully) last resort. The other techniques (shielding and ferrite cores) are usually easier.

 

[nbucska]

The IPS is supposed to sense mechanical motion which is
MUCH slower than the noise from the W-T. If shouldn't be too hard to reject the later.


Plesae read FAQ240-1032
WEB: <

http://geocities.com/nbucska/>

 

[rauthr80]

Thanks for your reply.
We used one bypass capacitor across prximity (100pf), along with shielded cable. But when we bring wakytalky near sensor, the sensor acting as an anntena and switching the realy in speed switch.