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I am selecting a platinum thin-film RTD for a sensing application. I have settled upon TE Connectivity's PTF Family. Within this family, there are two different options for lead-wire composition:

  • Silver (Ag) wire
  • Gold (Au)-coated nickel (Ni) wire

The cost differences between these two options are negligible. However, considering Digi-Key and other suppliers actually bother to stock both options, I figure that which one you choose must make a practical difference—I just don't know what it is.

What are the relevant differences between these two different lead-wire compositions? That is, what are the advantages and disadvantages of each type of lead-wire, and when would you choose one over the other?

Additionally, should I expect to encounter any issues if I solder these leads onto a typical stranded copper wire (so that I can integrate them into a single connector, which plugs into my data-acquisition hardware)? I would be planning to use a standard 60-40 tin-lead rosin-core solder. I am a bit concerned about the possibility of galvanic corrosion due to dissimilar metals. Is that a concern? Do I need a special type of solder? Is there anything else I should be concerned about? Are these types of RTDs usable for this type of application, or do I need to seek out RTDs with different lead-wire compositions?

(For the purposes of this question, please assume that the RTDs will be used in environments strictly < 100°C. I will not be getting anywhere close to the 200°C maximum range of a class AA (F 0.1) RTDs.)

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2 Answers 2

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Heraeus states: Connection techniques The preferred connection technologies are welding, brazing, or soft soldering, depending upon the lead wire and temperature rating of the element. Recommended connection techniques are specified on each thin film element data sheet. Generally, welding is recommended for Ni or Pt coated Ni lead wires, and soft soldering is recommended for silver alloy or gold-plated lead wires. For elements with gold-alloy lead wires, such as the C416 type, only solder alloys specifically designed for use with gold should be used. Other alloys not specifically recommended for use with gold wire may cause irreversible lead wire damage.

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  • \$\begingroup\$ This confirms that soft soldering is appropriate for both, and it also points out that I need a special type of solder alloy for the gold-plated nickel lead wires, so that seems like a good reason to exclude that option. Would you agree with that interpretation? It still doesn't clarify to me why both options exist, or what the advantages/disadvantages are. \$\endgroup\$ Mar 23, 2022 at 6:34
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    \$\begingroup\$ Please cite your sources, and use citation markdown for text that isn't your own writing. \$\endgroup\$
    – Mat
    Mar 23, 2022 at 8:05
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According to the manufacturer's data:

Wide operating temperature range: -50°C to +600°C (Ni/Au wire and Class F 0.3, Ag-Wire versions are limited to 300°C)

So if you needed to measure more than 300°C you should use the Ag type, which costs about 6% less in quantity. But you don't so you can use either. Presumably the gold-plated leads are for screw terminal use rather than soldering or welding.

For < 100°C your soft solder is fine for either type, at least that is my prediction. Nickel does not wet well with rosin flux, but the gold should take care of that long enough to get a good joint (before it all dissolves in the solder). Ag solders okay, but can tarnish in certain atmospheres.

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  • \$\begingroup\$ I was with you until the edit; now I am confused. You changed the recommendation in a way that now seems inconsistent with my reading of the quoted portion of the datasheet. \$\endgroup\$ Mar 23, 2022 at 5:08
  • \$\begingroup\$ @CodyGray I think it is correct now, even though it may seem unintuitive. But it's late. \$\endgroup\$ Mar 23, 2022 at 5:54
  • \$\begingroup\$ Ag is indeed cheaper in quantity, and I understand the claim that the gold-plated leads would be for screw terminal use, but the way I read the quoted portion of the datasheet, Ag leads are limited to 300°C, which means if I needed to measure >300°C, I should use the Au-plated Ni type, not the Ag type. I think that's where the edit went wrong. Either way, appears it doesn't matter for me, since (A) I don't need >300°C, and (B) I couldn't even if I wanted to, as I'm using the F 0.1 accuracy, which don't go that high. Though it makes me wonder why the F 0.1 variants come in both wire types… \$\endgroup\$ Mar 23, 2022 at 6:20

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