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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Thu Jan 11, 2018 3:31 pm Post subject: Sensor Wire(s) Shield (eg O2) Alternatives? |
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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.
_________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN
Last edited by Vanagon Nut on Sat Jan 13, 2018 6:40 pm; edited 1 time in total |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4800 Location: Bemidji, MN
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Posted: Thu Jan 11, 2018 5:00 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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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 |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Thu Jan 11, 2018 8:24 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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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 |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4800 Location: Bemidji, MN
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Posted: Thu Jan 11, 2018 8:50 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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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 |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4800 Location: Bemidji, MN
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Posted: Thu Jan 11, 2018 8:50 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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oops. i see "O2" in the title!!
-dan |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4800 Location: Bemidji, MN
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Posted: Thu Jan 11, 2018 9:03 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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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 |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Thu Jan 11, 2018 9:06 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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DanHoug wrote: |
oops. i see "O2" in the title!!
-dan |
edited
Heh. No prob.
Ya, O2, RPM (crank sensor) and knock sensor signals. I tried to make this topic applicable to the WBX as well so didn't spec the other inputs.
I know the cable can be had but haven't found a local or Canadian vendor who sells by the foot. Someone kindly pointed me to an aviation parts supplier. I should email and see what the actual shipping cost is to Canada.
22 AWG though (but it may be doable. The O2 heater element would likely be the biggest draw item. Bentley shows 1.0 metric, so 18 AWG, for nearly all the wires involved)
http://www.bandc.aero/22awgshieldedtriowhitetefzelwire.aspx
"INTERNATIONAL CUSTOMERS
We strive to give you the best possible pricing on shipping. Any order shipped outside of the continental United States may encounter significantly higher costs. PLEASE call if you need the exact amount for shipping."
Neil. _________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Thu Jan 11, 2018 9:15 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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DanHoug wrote: |
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 |
thanks
I think for this engine (jetta engine swap) VW used the same size 1 metric wire gauge for all 3 sensors involved simply b/c 1 metric was large enough for the O2 heater current draw. IOW, why would they source 2 different gauge cables.
I'm being kind of fussy here by replacing these corroded wires but as per your comments, the O2 and knock sensor both put out very low voltages so.... Not sure about the RPM sensor but i assume it's an inductive type pickup that generates a square wave on/off type thing so its' voltage output would also be in the millivolt range.
Neil. _________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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SteveMc Samba Member
Joined: December 19, 2013 Posts: 210 Location: Alberta, Canada
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Posted: Thu Jan 11, 2018 9:18 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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Vanagon Nut wrote: |
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 |
Take a box of doughnuts to your local Westburne electrical supply and they likely will go into the yard and chop off the length you need. What you are describing sounds like a pretty common cable. _________________ 1986 Transporter Single Cab Syncro |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Thu Jan 11, 2018 10:12 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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SteveMc wrote: |
Take a box of doughnuts to your local Westburne electrical supply and they likely will go into the yard and chop off the length you need. What you are describing sounds like a pretty common cable. |
Ya, you'd think. The local Eecol shop didn't have anything and I'd have to buy the entire roll/box if they brought it in. _________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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rmcd Samba Member
Joined: October 29, 2010 Posts: 1349 Location: PNW - its a dry rain.
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t3 kopf Samba Member
Joined: October 22, 2012 Posts: 1115 Location: over by 'der
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djkeev Samba Moderator
Joined: September 30, 2007 Posts: 32634 Location: Reading Pennsylvania
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4800 Location: Bemidji, MN
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Posted: Fri Jan 12, 2018 7:49 am Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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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 |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Fri Jan 12, 2018 2:47 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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DanHoug wrote: |
just a word on knock sensors and wiring...
- 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.
-dan |
I have no idea if what Dan wrote makes this a moot point but from what I've read, knock sensor bolt torque value is somewhat critical to sensor performance and longevity.
As to wire sources, kind of embarrassing but links below are from a 'motor sport' wiring harness link I posted here. It appears http://prowireusa.com/ sells this cable by the foot:
http://www.prowireusa.com/c-58-shielded-tefzel-cable.aspx
http://www.prowireusa.com/c-158-shielded-ml-cable.aspx
Not exactly sure how this "drain wire" connector secures to the shielding but I think it is soldered on:
_________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4800 Location: Bemidji, MN
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Posted: Fri Jan 12, 2018 4:02 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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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 |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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Posted: Fri Jan 12, 2018 5:01 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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DanHoug wrote: |
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 |
Thanks. I see conflicting info on how that terminal is fastened. Yes that wire is likely overkill; these sensor wires won't be too close to engine or exhaust. But then as a point of reference, grey striped "engine" split loom is rated at ~ 150º C max so..... < shrugs >
In metric, if I'm not mistaken:
O2 signal 1.0
O2 heater 1.0 (controlled by "HO2S module")
RPM 1.0
Knock 0.5
I'm curious if I could run a physically separate unshielded high temp 2 conductor cable to O2 heater. That way I could just buy one length of 3 conductor 18 AWG; as a WAG, I doubt the larger gauge would adversely affect the knock sensor circuit.
Assuming unshielded O2 heater wires risk picking up RF, would that transfer to O2 element? But then the WBX uses separate wires for the O2 heater......
Yes I'm over thinking this!
_________________ 1981 Westy DIY 15º ABA
1988 West DIY 50º ABA
VE7TBN |
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Vanagon Nut Samba Member
Joined: February 08, 2008 Posts: 10379 Location: Sunshine Coast B.C.
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DanHoug Samba Member
Joined: December 05, 2016 Posts: 4800 Location: Bemidji, MN
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Posted: Fri Jan 12, 2018 10:09 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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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 |
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t3 kopf Samba Member
Joined: October 22, 2012 Posts: 1115 Location: over by 'der
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Posted: Fri Jan 12, 2018 10:56 pm Post subject: Re: Sensor Wire(s) Shield (O2): Soft M Copper Pipe? |
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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. _________________ '90 Carat w/ '95 phase 1 EJ22 OBD2 conversion |
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