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I'm laying down a number of temp sensors to the air exchange machine with heat pump. Temps there wary from -35 to +70 celsius. I may like to change/relayout components in the machine, therefore need some degree of flexibility to the layout and therefore decided to use connectors.

My choice is ended at Molex SL gold plated terminals. And wiring scheme to be daisy chain, as shown at the attached figure.

I'd like to ask advice/confirm my thinking about these two matters:

  1. I was thinking to use 2 conductor + braid for the cable. Having braid to be used as ground. Is that right choice? Some time ago I met somewhere a recommendation to use ground + signal conductors in a twisted pair. Would it mean that vcc would go to the braid in my case? Or, should I get a twisted triple + braid? (then I'd need to get 4pin housings for the terminals?). Or, should I care about it at all because total length of all cables will be below 30 meters?

  2. Is it OK to get tin plated wires to crimp with https://www.molex.com/molex/products/datasheet.jsp?part=active/0016020097_CRIMP_TERMINALS.xml&channel=Products&Lang=en-US#partdetail Googling this did not bring me any concrete answer besides that tin + gold is a bad combination and will corrode even quicker than tin-to-tin connectors.

Like a mentioned, I'd like this to last for years. Therefore paying attention to this details. Though, due to being novice in electronics may be choosing expensive & inefficient solutions.

wiring principle

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  • \$\begingroup\$ Max distance is 1 meter. Between both sockets as well as socket-to-socket cables \$\endgroup\$
    – user431529
    Commented Jan 22, 2019 at 4:52
  • \$\begingroup\$ well, your answer is open ended meaning it requires me to understand the subject. But like I wrote, I'm novice to the electronics and such not able to make right conclusions based on physical/electrical properties of the components. I asked two questions in the post. But I did not find the answer in your answer. Or, did I miss it? \$\endgroup\$
    – user431529
    Commented Jan 22, 2019 at 6:45
  • \$\begingroup\$ you missed it. Use Gold-Gold and consider the other issues and suggestions \$\endgroup\$ Commented Jan 22, 2019 at 7:04
  • \$\begingroup\$ Ok. Gold-to-gold connectors. How about cable (Q1)? I'm sorry I am unable to catch an advice in your notes in regards of my setup. Do you think a shielded cable is necessary for reliable operation with my conditions? \$\endgroup\$
    – user431529
    Commented Jan 22, 2019 at 9:50
  • \$\begingroup\$ I don't know your noise conditions. Since you know nothing about crimp contacts, I suggest you buy USB cables or similar \$\endgroup\$ Commented Jan 22, 2019 at 14:35

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(Is) 2 conductor + braid cable ... the right choice?

  • Perhaps if it meets your specs for cost, flex and EMI reduction, environment and rodent-proof ? it all depends on many things unspecified

Is it OK to get tin plated wires to crimp?

Not for gold plated contacts. WHy do you think it is tin plated?

=========================================================

Read the "TIN Commandments"

Then you will probably choose only lubrication over Au plating over Ni plating.

I believe going up over 0'C increases the rate of condensation and oxidation from evaporation.

If this was for a hot surge connection, then I might suggest tin-tin contacts with cap discharge wetting the contacts clean each use.

Cables

  • Shielded twisted pairs (STP) is best for EMI CM rejection with the shield only terminated at the unit yet worst for high impedance "1-wire" bus length due to the added capacitance. So UTP gives faster rise times but lower immunity.

  • UTP capacitance is about 52pF/m at 1-Wire speeds limited by Vcc/R current T=RC and you need about 10x bit rate for rise time for best performance.

  • STP can be up to 325 pF/m which limits the rise-time x cable length product.

  • Unshielded twisted pair (UTP) may be considerably less cost for power and signals but may need more EMI testing for susceptibility from ambient transients, SMPS, motor noise, arc welders, distant lightning, ESD, etc. depending on your impedance imbalance.

For better immunity Bus drivers are used.

Maxim guidelines for cable

Connectors

Other choices are those commonly used for telecom such as RJ-11, RJ-45 with Au contacts.

ESD protection

Must be considered to limit current from hiV cable charged connections.

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    \$\begingroup\$ thank you for the post. Unfortunately that does not contain answers I'm looking for \$\endgroup\$
    – user431529
    Commented Jan 25, 2019 at 8:09
  • \$\begingroup\$ To answer your question " WHy do you think it is tin plated?". The cables I have are these: ebay.com/itm/201840047760 (Tinned Copper wires) \$\endgroup\$
    – user431529
    Commented Jan 25, 2019 at 9:20
  • \$\begingroup\$ OK tin plated copper wire is 10x better in high humidity and rain and subject to fretting oxide with gold plating if there is micro-vibration or motion under pressure yet a good crimp should be a tight fit to survive a 2kg pull test connector.com/gold-or-tin-versus-gold-and-tin \$\endgroup\$ Commented Jan 25, 2019 at 9:46
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Thank you, Sunnyskyguy EE75, for bearing with me. You brought up valuable information. But I still post answer in a separate post just for others to find it quicker.

Q1 (wiring): I did not get the answer yet. Will continue looking for it. That could be just a matter for design, and to provide a clear and simple answer more information is needed, as Sunnyskyguy EE75 mentioned.

Q2 (crimping gold plated terminal): I did not read product specification carefuly enough. There it says: plating

Which answers my original question: tin plated wire can be safely crimped with 16020097 terminal.

https://www.molex.com/webdocs/datasheets/pdf/en-us/0016020097_CRIMP_TERMINALS.pdf

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