Which bayonet probe, J or K

[ccsmith51]

I have what appears to be a Westach dual CHT/EGT gauge, although there are no markings on the gauge.

It has a ring sensor for CHT mounted under the #3 bottom plug. I'm considering replacing the ring sensor with a bayonet for better accuracy.

I see J and K sensors listed on ACS. How can I tell which I should use with this gauge?

[az_gila]

Originally Posted by ccsmith51

I have what appears to be a Westach dual CGT/EHT gauge, although there are no markings on the gauge.

It has a ring sensor for CHT mounted under the #3 bottom plug. I'm considering replacing the ring sensor with a bayonet for better accuracy.

I see J and K sensors listed on ACS. How can I tell which I should use with this gauge?

Look at your existing ring sensor leads.

White/Red is a J-type
Yellow/Red is a K-type

[ccsmith51]

Excellent, Gil, thanks!!!

[ccsmith51]

Originally Posted by az_gila

Look at your existing ring sensor leads.

White/Red is a J-type
Yellow/Red is a K-type

Looked today. There is heat shrink at the cable termination at the ring, so I can't see the colors. The two wires that come out of the braid where they connect to the gauge are black and white....

Would that be a J type?

[az_gila]

Originally Posted by ccsmith51

Looked today. There is heat shrink at the cable termination at the ring, so I can't see the colors. The two wires that come out of the braid where they connect to the gauge are black and white....

Would that be a J type?

Black/White is an alternative International color code for aa Type-J.

However, just to confuse us all --

Black translates to White
White translates to Red

Note the +/- signs

[ccsmith51]

Got it, thanks again.

[az_gila]

Originally Posted by ccsmith51

Got it, thanks again.

Another twist....

If it is an actual Westach CHT ring thermocouple, their catalog talks about a type J device, but then also talks about a "black sleeve" on the red wire of the J-type red/white leads.

Before you hook up the new CHT thermocouple cut the shrink tubing off both ends of the old thermocouple and check for wire colors...

[PaulT]

An easy way to tell if your sensor is J type (Iron/Constantan), is to test with a magnet. One of the conductors is Iron.
However the total lead and probe resistance is an important consideration with analogue (steam) thermocouple gauges, as are the extra joins you may have to introduce to achieve the length required.
The errors that these can cause may offset any advantage in using a better quality probe.
I would probably stick with the original.
Paul.

[rocketbob]

Westach uses J-type probes for their cylinder head instruments. Its more common to see K-type on both CHT and EGT probes. Some of their CHT instruments will work with both. I have a neighbor that had to replace some CHT probes with a Westach gauge, and I gave him some K-type probes. He called the factory and asked if they could be used and they said yes but wire them to a different terminal on the gauge.

[az_gila]

Originally Posted by rocketbob

Westach uses J-type probes for their cylinder head instruments. Its more common to see K-type on both CHT and EGT probes. Some of their CHT instruments will work with both. I have a neighbor that had to replace some CHT probes with a Westach gauge, and I gave him some K-type probes. He called the factory and asked if they could be used and they said yes but wire them to a different terminal on the gauge.

In some instruments, but they are not interchangeable. Given a choice, the J-type are better for CHT as they generate about more voltage than the K-type. Every bit extra helps when the measurement needed is of milliVolts.

They do not have as high an upper operating temperature limit, so type-K are needed for the hight EGT temperatures.