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PaxInstruments / t400-electronics

Electronics for the Pax Instruments T400 temperature datalogger
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What thermocouple connector to use? #92

Closed charlespax closed 9 years ago

charlespax commented 9 years ago

We need a good solution for the thermocouple connector.

I've been using these for prototyping. I like that they have good thermal contact with the board. The major issue with this is that it deforms. Some mini thermocouple connectors are slightly different and larger ones will deform the connector such that slightly smaller connectors will then no longer fit snugly in the connector. http://item.taobao.com/item.htm?spm=a1z09.2.9.200.riN5jg&id=19117501866&_u=n1ohf9gofd01 screen shot 2014-12-12 at 12 55 21

Keystone has one that could be good. I have tested similar ones from Taobao and have experienced the same deformation issue. We have ordered samples to see if the issue exists in the connector from a more reputable source like Keystone. I am, however, concerned about the thermal contact. http://www.mouser.hk/ProductDetail/Keystone-Electronics/3546/?qs=sGAEpiMZZMsQtlBhqKq43eLjyZA2RfTM screen shot 2014-12-12 at 12 54 15

Here is a mechanical drawing. screen shot 2014-12-12 at 13 07 29

The Keystone connector also comes in a double housing I think would work. http://www.mouser.sg/ProductDetail/Keystone-Electronics/3550-2/?qs=%2fha2pyFadugLYgmJwk1tv8qWCA0LET5NWQWQWxRitPI%3d screen shot 2014-12-12 at 12 59 52

Here is a mechanical drawing screen shot 2014-12-12 at 13 02 43

We can use a custom connector (https://github.com/PaxInstruments/t400-electronics/issues/17) if we can't find the right thing on the market. Here is the SolidWorks files in the repo. screen shot 2014-12-12 at 12 53 25

For reference, here is a mini thermocouple connector drawing from the datasheet in git. screen shot 2014-12-12 at 13 01 20

charlespax commented 9 years ago

The outside of the mini TC blades is 8+(2.4+3.7)/2 = 11.05 mm

The inside of the mini TC blaces is 8-(2.4+3.7)/2 = 4.95 mm

The outside of the connector is 8.9+4.57 = 13.47 mm

The inside of the connector is 8.9-4.57 = 4.33 mm

With these numbers the mini TC connector should happily fit in the female connector. Now the issue is the thickness of the mini TC connector.

charlespax commented 9 years ago

It looks like 0.64 mm is standard. I haven't seen other sizes. The mini TC connector is 0.8 mm, 25% thicker. screen shot 2014-12-12 at 13 18 13

charlespax commented 9 years ago

We cannot use the double connector. At 20.8 mm wide we would need 20.8*4 = 83.2 mm to fit four connectors between the LCD standoffs. We only have about 66 mm of space available. screen shot 2014-12-12 at 13 37 12

charlespax commented 9 years ago

We have 4.7 mm of clearance between the LCD housing and the PCB. The double connector needs 5.4 mm, so that won't work. However, the single connector needs only 2.49+1.57 = 4.06 mm between the PCB and LCD.

screen shot 2014-12-12 at 13 41 33

charlespax commented 9 years ago

After an initial round of casual testing I believe the Keystone connector will be unsuitable as the thermocouple connector. I plugged in several thermocouple connectors that were manufactured a bit differently from each other. The thicker male connector deformed the female connector, what was then too loose for the thinner male connector.

charlespax commented 9 years ago

We'll use the Keystone connector for Electronics version 0.10 then seek out a custom solution. Closing issue.

Custom connector issue: https://github.com/PaxInstruments/t400-electronics/issues/17