PIREP: newer JPI CHT piggyback sensor

[Bolter]

Background: I have a 4 channel JPI 700 in my J-model that was already installed when I bought the plane.  It had a spark plug ring gasket CHT sensor for the #3 cylinder.  For this year's annual, I decided it bothered me to have one cylinder reading 30-40°F high, and planned to install a JPI 5050-T sensor.  The 5050-T would install into the standard CHT sensor location, and allow attaching of the JPI and the factory leads.  When it came time to order it, I was referred to a replacement part number.  It seems the 5050-T is phased out for a new model, the M113-3/8".  The cost was the same ($105 at Spruce)

Description and Function: This new one looks like the spark plug gasket type except it is 3/8" and works on the factory CHT sensor and is crushed in between the sensor and the cylinder, similarly.  Today was my first flight with it, so I wanted to share that it works well.   My temp's are now effectively identical on all cylinders, confirming that the spark plug type CHT sensor runs higher than "reality".  And I feel a great relief looking at the JPI and seeing all things even, instead of ignoring a bad reading.  I think that especially for LOP'ers who depend on accurate data, this is a worthwhile upgrade from the spark plug gasket version.

Installation: Installation is a bit of a nuisance.  You need to install an insulated sleeve over the sensor to protect it from the heat of the exhaust (I am guessing the function based on the appearance) AND string the factory wire out at the same time.  I gave up, and put a slit in the insulated sleeve to allow sliding the sleeve over the sensor and provide a passage for the factory lead.  The JPI lead is strung along the long axis of the sensor and is easily routed away from hot parts and into the existing wiring bundles.   The JPI people have made it very easy if the factory CHT sensor has a built in lead coming straight off the top.  Assuming all Mooney's use the same setup as mine, prepare to be frustrated if you don't put the slit.  Also, remove the spark plug and get some room to work with.  You can work around it, but it is not hard to remove the plug and get some much appreciated room for your fingers.  In case it is not obvious, you will want to do this with both upper and lower cowlings removed, as well.  

-dan

[HopePilot]

Awesome news.  I'm going to have my checked too.  Did they have it in stock at Spruce or did you have to special order it?

[Bolter]

Quote: HopePilot

Awesome news.  I'm going to have my checked too.  Did they have it in stock at Spruce or did you have to special order it?

[AmigOne]

Dan,

I have the same JPI EDM700 set up as you did in Cyl# 3 but never saw in the installation instructions that it needed a sleeve to protect it from the heat of the stack.  The only sleeve and 2 black tiewraps that comes with he part is to protect the connection between the pigtail and the cable to the panel unit.   Jose

[jetdriven]

Tom, so you are saying that the ring terminal sensor crushed under the factory probe reads actual CHT? I was under the impression that it read 40f low.

We have a 3/8" ring terminal stype thermocouple under the factory CHT probe.  Its not the JPI, but a Type J thermocouple.

[Bolter]

Quote: AmigOne

Dan,

I have the same JPI EDM700 set up as you did in Cyl# 3 but never saw in the installation instructions that it needed a sleeve to protect it from the heat of the stack.  The only sleeve and 2 black tiewraps that comes with he part is to protect the connection between the pigtail and the cable to the panel unit.   Jose

[Bolter]

Quote: jetdriven

Tom, so you are saying that the ring terminal sensor crushed under the factory probe reads actual CHT? I was under the impression that it read 40f low.

We have a 3/8" ring terminal stype thermocouple under the factory CHT probe.  Its not the JPI, but a Type J thermocouple.

[Bolter]

Quote: jetdriven

Tom, so you are saying that the ring terminal sensor crushed under the factory probe reads actual CHT? I was under the impression that it read 40f low.

We have a 3/8" ring terminal stype thermocouple under the factory CHT probe.  Its not the JPI, but a Type J thermocouple.

[jetdriven]

Quote: tomcullen

The kit I just installed has a ring sensor read what I *expected*.  what I expected was to see 30-40°F lower than the reading from the spark plug gasket-type sensor AND matching the other 3 cylinders.   I had read on this site that the spark plug sensor tends to read high.  If others have experience that the CHT ring sensor reads low by the same amount, I should have seen an 80°F change instead of 40°F

Of course, being satisfied with a test that gives you what you expected and then drawing the conclusion you want to see can get you into trouble.   But in my experience, this is usually, right.  I am not sure what convenient independent measurement I could make to confirm actual CHT matches my new reading versus my old, higher reading with the spark plug sensor.    

The new sensor does contact the metal around the factory sensor.  It has the potential to be reading accurately.  I do not know what temperature gradient to expect between the tip of the factory sensor and the threads of the factory sensor.  

Your design sounds a lot like the JPI design.  Are you seeing low readings?

-dan

 

[AmigOne]

Tomorrow I will insulate the portion of the piggyback adapter to see if this affects the readout of the CHT.  However since this is the probe that goes to the analog factory CHT gauge I am not sure that I will be able to tell the difference unless it is a drastic one.  The factory CHT probe is not really "exposed" since it is mostly inside the piggyback adapter, at least, imho, not exposed in such a way as to affect the readout.  I will send some pictures so we can compare with your set up.

[AmigOne]

This is the picture of my piggyback.  Today I kind of insulated it with some baffling material and as expected I could see in the factory gauge no appreciable difference from previous readings or with the digital readout in the EDM.

[carusoam]

To solve this challenge You will need a second thermocouple down the well touching the same internal surface as the original bayonet sensor.

To do this, requires the T/C manufacturer to build two thermocouples into the one bayonet.  The best construction may still yield a 1oF difference in readings.  Better than the current difference, but not perfect.

This solution requires a new part number and some FAA paperwork. I can supply the design, can anyone here detail and supply the FAA paperwork?

Back in the day I worked on colocating pressure and temperature sensors for plastics machinery.  Good rheology data requires collocation of P and T sensors...

Unfortunately the pressure sensors I worked with could not handle ICPs....

With the number of pilots currently interested in this accuracy, this project makes sense.  The overall pilot population, maybe not asking yet. Time to supply some pressure to this heated discussion...

Let me know...

Best regards,

-a-

[Bolter]

Quote: AmigOne

This is the picture of my piggyback.  Today I kind of insulated it with some baffling material and as expected I could see in the factory gauge no appreciable difference from previous readings or with the digital readout in the EDM.

[jetdriven]

That looks pretty much like my ring terminal 12$ sensor under the factory well probe on #3.  I still wonder if it reads accurate CHT or 40f low.  We assume it reads 40f low.