1 Milliohm Current Sense Resistor: 3 of the 6 Fields a Sense Design Needs Appear on Zero of 234,815 Rows, Checked for Germany

A 1 milliohm current sense resistor in Walsin’s catalogue publishes three of the six fields a sense design turns on, and withholds three. We counted all 11,616 low-ohm rows. Maximum working voltage, pulse and surge capability and terminal construction have no column anywhere in the 137 chip resistor export files. Zero of 10,428 thick film rows reach 1 milliohm.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, read both low-ohm current sense exports from Walsin Technology (Walsin) for this post — Thick_Film_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx at 10,428 rows and Metal_Low_Ohm_Current_Sense_Chip_Resistor__1of1.xlsx at 1,188 — and cut them by resistance decade rather than by series name. Every part number below is real. We hold no datasheet for either family and we say so.

Which fields does a 1 milliohm current sense resistor actually publish?

Three of six. We opened all 137 chip resistor export files and the schema is ten columns wide on every one of them: part number, two series strings, size, resistance, tolerance, TCR, rated power, packaging and termination. Three of the six fields a shunt design turns on have no column at all, across all 234,815 part numbers.

Field a sense design turns on	Column in the export?	Rows that publish a usable value, of 11,616
Rated power	Yes	11,616
Tolerance	Yes	11,616
TCR	Yes	11,492 — 124 rows state it as a one-sided range
Maximum working voltage	No column	0
Pulse or surge capability	No column	0
Terminal construction	No column	0

The Termination column exists and it is not the terminal construction. We checked all 11,616 low-ohm rows: it reads Sn base (Lead free) on every single one. That is a plating finish. Whether the part is two-terminal or four-terminal, whether the sense path is Kelvin-separated, and what the terminal resistance contributes at 1 milliohm are three different questions, and the export answers none of them.

We have not seen this counted anywhere. At 1 milliohm the terminal contribution is a material fraction of the total, and it is the field the catalogue is silent on.

Does Walsin’s thick film current sense line reach 1 milliohm at all?

No. Zero of 10,428 rows. We measured the minimum resistance in the thick film file at 0.005 Ω — 5 milliohm — and it is carried by exactly two part numbers, WW15WR005FTL and WW15WR005JTL, both on the 0815 footprint, which holds four part numbers in the entire 234,815-row catalogue.

So the decision at 1 milliohm is not thick film against metal. There is no thick film option. We counted 48 part numbers at exactly 0.001 Ω across both files and all 48 sit in the metal plate and metal foil export. Below 1 milliohm there are 10 more, down to 0.0005 Ω, and again all 10 are metal.

Resistance	Thick film rows	Metal rows	Lowest case size present
Below 0.001 Ω	0	10	0612 (1632)
Exactly 0.001 Ω	0	48	0306 (0816)
0.001 Ω to under 0.010 Ω	2	549	0306 (0816)
0.010 Ω to under 0.100 Ω	1,625	569	0201 (0603)

How many distinct specifications are actually on offer at 1 milliohm?

21, not 48. We grouped all 48 part numbers at exactly 0.001 Ω by every field the export publishes — size, tolerance, TCR and rated power — and they collapse to 21 distinct signatures. 27 of the 48 part numbers are indistinguishable from at least one other on every published field.

Eight of those 21 signatures carry four part numbers each. The 2512 group at ±1%, ≦±70 ppm/°C and 2 W is one of them.

Walsin part number	Case size	Resistance	Tolerance	TCR	Rated power	Match / mismatch vs WW25NR001FTL
WW25NR001FTL	2512 (6432)	0.001 Ω	±1%	≦±70	2 W	Reference row
WW25KR001FTL	2512 (6432)	0.001 Ω	±1%	≦±70	2 W	Match on every published field. The only difference is the Series string, and no column separates them
WW25KR001FTLJ	2512 (6432)	0.001 Ω	±1%	≦±70	2 W	Match on every published field. Series reads automotive; AEC-Q200 status has no column in the export
WW25NR001FTLJ	2512 (6432)	0.001 Ω	±1%	≦±70	2 W	Match on every published field. Series reads automotive, nothing else moves
WW12RR001FTL	1206 (3216)	0.001 Ω	±1%	≦±70	1 W	Match on resistance, tolerance and TCR. Mismatch on case size and rated power
WW25YR001FTL	1225 (3263)	0.001 Ω	±1%	≦±100	2 W	Match on resistance, tolerance and rated power. Mismatch on case size and TCR
WW15WR005FTL	0815 (2037)	0.005 Ω	±1%	≦±200	1 W	Match on tolerance only. Mismatch on resistance — five times the value, and the lowest the thick film file reaches
Your incumbent shunt	—	—	—	—	—	Fill this column from your own datasheet, then confirm against both sheets and qualify in your own circuit

Four part numbers, one published specification. If your approval process keys on the part number rather than the signature, you have four approvals to maintain for one electrical position — and if it keys on the signature, you cannot tell the automotive-named rows from the commercial ones without reading the Series string, because no qualification column exists.

Does a tolerance tighter than 1 percent reach 1 milliohm?

No. We counted all 11,616 low-ohm rows and found 32 at ±0.5%, every one of them in the metal foil series, and their resistance floor is 0.005 Ω. Not one of the 58 rows at or below 1 milliohm publishes a tolerance tighter than ±1%.

That is a decade of separation between two shelves that a selector presents as one range. The tolerance shelf stops at 5 milliohm; the resistance shelf runs to 0.5 milliohm. Across the 48 rows at exactly 1 milliohm, the tolerance field takes two values — 25 rows at ±1% and 23 at ±5% — so it discriminates, but only coarsely. WW25YR005DTL at 0.005 Ω and WW12DR010DTL at 0.010 Ω are two real ±0.5% parts, and both sit above the decade you are trying to design in.

Does the published field count change as the resistance decade falls?

The count of columns does not. What falls is how much each column discriminates. We grouped all 11,616 rows into four decades and counted, in each, how many part numbers are indistinguishable from another on resistance, size, tolerance, TCR and rated power together.

Resistance decade	Rows	Distinct resistance values	Distinct published signatures	Part numbers indistinguishable from another	Share
Below 0.001 Ω	10	2	6	4	40.0%
0.001 Ω to under 0.010 Ω	551	9	257	294	53.4%
0.010 Ω to under 0.100 Ω	2,194	50	1,608	586	26.7%
0.100 Ω to under 1 Ω	8,861	124	4,863	3,998	45.1%
All low-ohm rows	11,616	172	6,734	4,882	42.0%

4,882 of 11,616 low-ohm part numbers cannot be told apart from at least one other part number using any field Walsin publishes. That is the real answer to what you can decide from published data: at 1 milliohm you can decide a footprint, a tolerance band, a TCR grade and a wattage, and you cannot decide anything else without a datasheet.

We also re-measured the TCR distribution for this post and it reproduces what we published earlier: zero of 10,428 thick film rows reach ±50 ppm/°C, while 612 of 1,188 metal rows do. That figure is ours and already live on this site; the decade cut above is new.

Do the tolerance letter and the tolerance column ever disagree?

On 3 rows. We checked all 11,616 low-ohm rows and could read a tolerance letter off the tail of 11,014 of them; the other 602 carry an embedded space that changes the tail, and we excluded those rather than guess. F reads ±1% on 5,755 rows, J reads ±5% on 5,224 and D reads ±0.5% on 32. Three rows contradict the convention, and two of the three sit on the four-part 0815 footprint.

Part number	Suffix letter	Tolerance the letter implies	Tolerance column reads	Match / mismatch
WW15WR005FTL	F	±1%	±1%	Match — the control row
WW15WR005JTL	J	±5%	±1%	Mismatch — one of only two thick film rows below 0.010 Ω
WW15WR010FTL	F	±1%	±5%	Mismatch — the same pair, inverted
WW20MR015FTL	F	±1%	±5%	Mismatch — the only metal row that disagrees, at 0.015 Ω, 2010

Two of the four part numbers on the rarest footprint in the catalogue carry a tolerance the suffix letter does not support. Treat both figures as unconfirmed until Walsin resolves them, and do not script a tolerance filter off the suffix letter.

What should a buyer in Germany do with a 1 milliohm sense position?

Four steps. The first costs nothing and the second removes the most common error we see. Walsin’s chip resistor export carries no column anywhere for RoHS status, REACH, lifecycle, lead time, operating temperature or qualification status, so none of those can be answered from the catalogue either.

1. Stop looking for a thick film option at 1 milliohm. There is none — zero of 10,428 rows. The shelf is metal plate and metal foil only.
2. Ask for the construction before the price list. Terminal count, Kelvin sensing and pulse capability are the three fields that decide a 1 milliohm design and none of them is published. Ask us and we will tell you what we hold and what we do not.
3. Cross the whole bill of materials in one pass. Paste up to 500 part numbers or drop your Excel or CSV into the free cross-reference tool, filter by commercial or automotive grade, and read every stated difference rather than a claimed match.
4. Check what is physically in Hong Kong on ready stock before committing a build slot — a dated snapshot as at 23 September 2026, not a live feed, and chip resistor stock representation is 0.11% of the catalogue.

For the construction comparison at series level, see thick film against metal plate, and for the full TCR distribution, zero of 10,428 reach 50 ppm. The line is on the Walsin chip resistor page.

The short version

A 1 milliohm current sense resistor publishes three of the six fields the design turns on. Maximum working voltage, pulse capability and terminal construction have no column in any of the 137 chip resistor export files, across all 234,815 part numbers, and the Termination column reads the same 19 characters on all 11,616 low-ohm rows. Zero of 10,428 thick film rows reach 1 milliohm; all 48 rows at exactly 1 milliohm are metal and they collapse to 21 distinct published signatures, so 27 of the 48 are indistinguishable from another part number on every field. Across the whole low-ohm set, 4,882 of 11,616 part numbers are. Tolerance tighter than ±1% exists on 32 rows and stops a decade above 1 milliohm. We hold no datasheet for either family. Qualification stays with you.

Send us the 1 milliohm positions off your German bill of materials and we will tell you which published signature each part number belongs to, which other part numbers share it, and what was physically in Hong Kong on 23 September 2026. If your shunt approval rests on a maximum working voltage, where did that number come from?

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Frequently asked questions

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