Sensor Wire(s) Shield (eg O2) Alternatives?

[Vanagon Nut]

Hi folks.

For various reasons, I've been trying to locally source a multi conductor shielded cable suitable for use with engine sensors. No luck. A post here regarding replacement of the green O2 WBX wire showed hand wrapped braided copper wire and another suggested foil (tin foil?) as shield. Securely attaching the "drain" wire to foil shield would be a challenge and braiding copper strands by hand would take some time though at this point, I'm willing to try those options.

I know this sounds crazy, but what about using 1/4" or 3/8" M thin wall pipe as the shield? Or would engine bay heat build and transfer via the copper and damage the wire casing?

Soldering the shield "drain" wire (no pun intended) to copper would be easy but cable routing would likely be limited to mild bends or largish radius bends. Conductor(s) could be shrink wrapped? Sealing the ends would be imperative.

Thoughts?

Neil.

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1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[DanHoug]

all sorts of choices... what you want to search for is 'shielded twisted pair'.

one choice is CAT6 cable.. you can get it in tough shell configurations, stranded for flexibility, flooded for water resistance. but really, i had some plain ol' CAT5E hanging under my van for years and it was just fine. if it does fail, dirt cheap to replace.

i've got a coil of shielded, multi-pair control wire from a friend used for industrial control. about a 1/2" cable with many pairs.

Belden makes an array of shielded, non-paired wire in various gauges and conductors.

go to digikey.com or mouser.com and search for wire>shielded> then name your configuration. both companies 100% reliable to order from.

-dan

[Vanagon Nut]

Thanks Dan.

I've been searching quite a bit, emailing, calling. So far, all the local vendors [edit: and it appears, online vendors like mouser **] want me to buy a roll or box of the cable I want (e.g. -20º - 105º C). Landing a US sourced cable would likely be relatively costly. Good to know the CAT cable you ran held up. My concern is engine heat.

Neil.

** https://ca.mouser.com/Wire-Cable/Multi-Conductor-P...rpZ1yx79kq
_________________
1981 Westy DIY 15º ABA

1988 West DIY 50º ABA

VE7TBN

[DanHoug]

if you can keep it away from the manifolds, the PVC insulation will hold up just as well as other wires in the engine bay.

here's a link to some Belden control cable that is shielded:
https://www.belden.com/products/industrial/cable/instrumentation-cable/pltc-cable

but depending upon what you are trying to monitor or send data for, shielding really may not be required. for gauges, cruise control, temp monitoring, etc, it isn't needed at all. even the wiring to the ECU isn't shielded (exception O2 output), and that has digital control circuits that can be susceptible to RFI.

what are you wanting to transmit?

-dan

[DanHoug]

oops. i see "O2" in the title!!

-dan

[DanHoug]

if this is for O2 sensor metering i'd be tempted to try the Belden 9451SB. the SB version stands up to 105C temp on the jacket. i use the 9451, not SB, for control circuits in facilities i wire and it's pretty tough, more so than CAT cable but is only rated for 60C.

the 9451 cable capacitance is such that it shouldn't cause issues with the high impedance output of the O2 sensor.... essentially the sensor doesn't want to be loaded down and push against excessive capacitance.

-dan

[Vanagon Nut]

[Vanagon Nut]

[SteveMc]

[Vanagon Nut]

[rmcd]

Here are a bunch of options. Most sold by the foot.

https://www.aircraftspruce.com/menus/el/wire.html
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VW LT40 build. Like a Vanagon but 30% larger in every direction and 40% slower even in metric.
https://www.thesamba.com/vw/forum/viewtopic.php?t=749359&highlight=

[t3 kopf]

Digikey sells shielded wire in several gauges. Here is 18 guage shielded wire sold for $2.20 a meter

https://www.digikey.com/product-detail/en/tensility-international-corp/30-00335/T1248-1-ND/5270182

*edited to add link
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'90 Carat w/ '95 phase 1 EJ22 OBD2 conversion

[djkeev]

While the center core is not stranded, Hence subject to long term hardening and fatigue, I would think that a length of cable TV coax would work just fine for a long time.

Dave
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Ghia
http://www.thesamba.com/vw/forum/viewtopic.php?t=392473

Vanagon
http://www.thesamba.com/vw/forum/viewtopic.php?p=6315537#6315537

Beetle
https://www.thesamba.com/vw/forum/viewtopic.php?t=482968&highlight=74+super+vert

[DanHoug]

just a word on knock sensors and wiring... the sensor is a very common piezo disc transducer. the same type of element is used in musical instrument pickups. they have 2 electrical characteristics that come into play..

- like a guitar with a piezo pickup, the sensor wants to have its output attached to a high impedance INPUT. this is taken care of by the manufacturer in the design of the ECU it plugs into and there's nothing we can do or not do for this.

- because of the high impedance OUTPUT of the sensor, it is susceptible to the capacitance of the cable transmitting the signal. one can literally hear the difference between different guitar cable simply because of the effect of the cable on the signal. fortunately, the voltage generator by a piezo sensor is quite large and the ECU is tuned to 'listen' to a narrow frequency range for knocking. so even tho the cable choice will introduce distortions, the system will be fairly tolerant of these distortions.

since the sensor is essentially picking up ALL sounds in the audible frequency range, the art in designing knock sensing systems is to shape the ECU algorithms to ignore all the other engine sounds except a unique signature waveform created by detonation.

the short story is that guitar cable would be perfect for knock sensor signal transmission! well, were it not for the oil/temp/physical resistance needed for engine bay wiring. pretty much any shielded cable should work. i coulda just said that in the very beginning but if you have a choice, always go with the lower capacitance cable if they publish that spec.

-dan

[Vanagon Nut]

[DanHoug]

that looks like a crimp connection with heat shrink, but can't quite tell.

that MIL spec wire would be fine, but might be overkill. what is your conductor list for the cable you're looking for?

-O2 signal 1
-O2 heater 2
-knock 1

etc

[Vanagon Nut]

[Vanagon Nut]

[DanHoug]

yeah, keep it simple and see if it works. bolt torque on the sensor is designed to not split the fragile piezo element but also afford a good sonic connection. tighten it "good enough" and you'll be fine.

if you get a multi-pair cable shielded cable, running the DC alongside the the sensitive circuits more than likely won't be an issue at the amperage the heater circuit uses. and many multi pair shielded cables have each pair shielded.

consider this... shielding in many instances is over-rated and can actually act an an antenna and dump more RF into a circuit if not properly terminated. some instances require the shield to be grounded at both ends, some only at one end, depending upon the issue of forming ground loops.

just try something and see if it works. i think you'll be surprised at how much you can get away with. i deal with 100,000 watt transmitters radiating into the 'transmitter shack' where all sorts of control circuits, digital and analog reside. yes, there can be issues but you can get by with many things. lightning grounding being the exception..

-dan

[t3 kopf]

The wire I posted is the stuff VW used for the WBX 02 sensor and the stuff I use on my 95 subie 2nd 02 sensor, which I am using a stock 3 wire bosch 02 sensor for. Most sensor wires in a subie harness are smaller than 18 gauge. Its a pretty easy solution that works.
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'90 Carat w/ '95 phase 1 EJ22 OBD2 conversion