Original CHT gage in M20E - RTD or Thermocouple?

[nevadabandit]

The JPI in our plane uses the thermal wells on each cylinder for CHT, therefore the original primary gage has no sender or probe.

We want to use a plug probe on one cylinder to provide a signal to the original Mooney gage in the panel.

We tried a plug probe but it did not respond correctly, just read nothing or pegged the gage. We are suspect that the original probe was an RTD and not a thermocouple.

Is there an RTD available that is in the plug probe configuration available?

The reason for all of this is our inspector indicated that the primary gage must function and that the JPI cannot be the only indication for CHT

Can you shed some light on this situation? 

[kortopates]

If you have a EDM-7xx or -8xx monitor, legally the factory CHT probe has to remain in the cylinder well, and the JPI will use one of three possible gasket probes including possibly one at the base of the factory probe.

If you have an EDM-9xx monitor, which is approved for primary, then the factory CHT instrument is removed from the aircraft.


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[N201MKTurbo]

Your original was probably a thermistor. So not a thermocouple or RTD. 

The usual drill is to leave the original sender in place and use a spark plug ring for the advisory scanner. If you aren’t using a scanner that is approved for primary, you have to leave the original probe and gauge in place.

[Echo]

1 hour ago, kortopates said:

If you have a EDM-7xx or -8xx monitor, legally the factory CHT probe has to remain in the cylinder well, and the JPI will use one of three possible gasket probes including possibly one at the base of the factory probe.

If you have an EDM-9xx monitor, which is approved for primary, then the factory CHT instrument is removed from the aircraft.


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NOT CORRECT!  The cylinder temp on 730-830 is Primary. Put a piece of tape over the OEM indicator. 

[PT20J]

I believe the 7xx and 8xx are all approved under the same STC.

 

[kortopates]

1 hour ago, Echo said:

NOT CORRECT!  The cylinder temp on 730-830 is Primary. Put a piece of tape over the OEM indicator. 

No not the 730 and 830's but perhaps you were thinking of the EDM-711. The 711, which is I see very very few of is indeed certified as primary for EGT, CHT and OT. But not the very popular 730 & 830.

[Echo]

6 hours ago, kortopates said:

No not the 730 and 830's but perhaps you were thinking of the EDM-711. The 711, which is I see very very few of is indeed certified as primary for EGT, CHT and OT. But not the very popular 730 & 830.

No.  Seriously, STOP spreading misinformation.  I bought an 830.  It 100% IS primary for cylinder temp.  Do some research.  Also Oil Temp.  BOTH of these gauges can be taped LEGALLY with the EDM830.

[Echo]

32 minutes ago, Echo said:

No.  Seriously, STOP spreading misinformation.  I bought an 830.  It 100% IS primary for cylinder temp.  Do some research.  Also Oil Temp.  BOTH of these gauges can be taped LEGALLY with the EDM830.

 

[EricJ]

9 minutes ago, Echo said:

 

Unfortunately the STC language supercedes an internet ad, and the STC indicates otherwise as previously shown.   Can you show some actual authorizing paperwork that allows an 830 to be used as primary?

[BrentS]

Sorry to burst your bubble, and not to be mean in any way, but aviation consumer is not the final say for any aircraft equipment.  the faa approved the STC for the edm 730/830 as it is shown above by PT20J's post.  the edm 730/830 are secondary instruments, the edm 900/930 are primary instruments.

[N201MKTurbo]

11 minutes ago, Echo said:

 

Text in a catalog is not approved data. The STC from EDMs website is shown above by @PT20J. Unless you can find approved data that shows otherwise, your catalog listing is wrong.

[Echo]

O.K.  Crow eaten.  I have no plans to remove existing OEM gauge cluster.  So, NOT everything you read on the internet is true.  Sorry for my comments Paul and thank you for not calling me out as the dumb@$$ I clearly was on this.  Lesson learned.  Defer to those with a LOT MORE knowledge than me.  Scott

[Greg Ellis]

A little late to the game here (and I see it has been resolved), but I was curious about the EDM 730 and 830 being primary.  This is direct from JPI.

Hello Greg,

No, the EDM 730 and 830 are advisory instruments only. Primary ship’s gauges are required to remain in place and be operational.

Regards,

 

Branch Talley

JP Instruments, Inc.

[PT20J]

On 10/23/2023 at 10:17 AM, nevadabandit said:

The JPI in our plane uses the thermal wells on each cylinder for CHT, therefore the original primary gage has no sender or probe.

We want to use a plug probe on one cylinder to provide a signal to the original Mooney gage in the panel.

We tried a plug probe but it did not respond correctly, just read nothing or pegged the gage. We are suspect that the original probe was an RTD and not a thermocouple.

Is there an RTD available that is in the plug probe configuration available?

The reason for all of this is our inspector indicated that the primary gage must function and that the JPI cannot be the only indication for CHT

Can you shed some light on this situation? 

I'd call a MSC and find out the manufacturer and part number for the probe. It may be in the IPC or service manual, but sometimes they only show only a Mooney part number. Someone like Dan Riesland at LASAR or Don Maxwell may know the vendor part number. After you get the OEM gauge working, you have the choice of connecting the engine monitor #3 input to either a spark plug ring thermocouple or a smaller ring thermocouple that fits under the bayonet socket for the factory probe. The spark plug thermocouple will usually read about 20 deg F high and the bayonet will read about 20 deg F low compared to the factory gauge.

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