Thermocouple failures

nicely done.

GA

milo

Dear Brother,

Good Morning.

1. No, you can't solder the TC junction. Instead there is a process called Brazing to make the thermocouple juctions.

2. Further kindly check the TC housing material and cross check with gen. vendor to ensure that there is no failure.

Regards,

Hi,

As I understand, K type thermocouples are for higher temperatures and soldering in any form shall not last. You should specify the kind of damage if it is mechanical like perforation/wear etc. or electrical to know the answer.

karan

If you are experiencing repeated failures with a thermocouple style, I suggest you perform a failure analysis to determine the root cause of the failure. Then you will be able to engineer a fix. You might also contact Nanmac Corp. in Massachusetts. They have applications engineers with much experience. I can inform you in advance, that it is important to know whether you require the junction to be grounded or isolated.

Hi,

My suggestion is you go for below thermocouple as per following Spec.

1) T/C Sheath material as Inconel-601

2) T/c Junction : Ungrounded

3) Thermowell material : Inconel-601

u sholdn't go for SS material as they work upto 800 deg C. While Inconel can work upto 1200 deg C.

I assume that the thermocouple is mounted in a housing. Insure that the housing is sealed from exhaust gases. While a K thermocouple can withstand most typical exhaust temperatures, some components of Diesel exhaust may be corrosive. I would try to isolate the failure--is the thermocouple junction failing, or, perhaps more likely, some part of the interconnect is failing.

You may want to try a different sensor. Hi-Stat and others offer a high-temperature Pt RTD-based sensor.

http://www.stoneridge.com/index.aspx

My first guess is that your thermocouples are failing due to excessive vibration. The temperatures in an engine exhaust are nowhere near the maximum temperatures for a Type K.

The second guess is that you are getting inferior quality thermocouples.

...any danger of fault if the soldered end touched the thermowell surface?

Most thermocouples actually touch the thermowell (actually, called a sheath). This is called a grounded thermocouple. They react faster to a temperature change and, generally, more accurate than the ungrounded version. You need a transmitter/indicator that is specifically designed to use these types of thermocouples.

There is a third type of thermocouple, the exposed type. In this one, the thermocouple itself is actually unprotected and exposed (hence, the name) to the temperature being measured. These are usually used for low or normal room temperature, low oxidizing atmospheres.

I presume you are using the correct Ni-Cr / Ni-Al thermocouple wire and the the same material connection links between the wire and thermocouple leads (unless welded).