Are these ok? EDM 700 installation

[Tommy]

After 6 hours of owner assisted installation, I am now flying with an EDM 700! All went incredibly smoothly but when I was busy doing the panel and circuit breakers my engineer did these.

First the plastic cable tie on a shiny metal tube - presumably air inlet tube which he claimed to be the coolest part of the engine so no issues (see photo). Is that right?

Secondly, he didn't trim away excessive wire. Instead he wraps them up and tied them (see second photos) will this have any impact on the CHT/EGT readings?

[DaV8or]

I don't know if I would tie to the intake manifold, but I don't see any harm in it. They don't get hot. In the case of the excess wire, what he did is exactly correct. You do not want to trim them to length. Differing lengths of wire would alter the resistance value of the sender and give less accurate comparative readings. All looks OK too me.

[N601RX]

The length on thermocouple wires doesn't affect the readings. I rolled up a service loop behind the panel and cut them to length under the cowl.

[Awqward]

Good job Tommy....I was quoted 64 man hours to install a CGR-30P here in the UK at $120/hr.....needless to say didn't do that...

[Tommy]

Bit of conflicting information! I think the installation manual says the length of the wire doesn't affect the readings. I just thought it's unsightly and adds extra weight!

64 hours??!! You mean exactly the same it takes for Mooney China factory to built a M10?

[N601RX]

Thermo couples work by producing a small millivolt signal at the junction.  This small signal travels up the wire to amplifier/conditioner.  The front end of the conditioner is usually very high impedance op amps configured as in instrumentation amplifier.  Because the input impedance (usually 50mega ohm range) is so high there is no measurable voltage drop along the wires.  Longer wires are more prone to pick up noise.

[Guest]

There are many ways to complete the installation. Personally I never aim the EGT probe toward the spark plug. I try to make every installation user friendly to other maintenance tasks. Removing plugs risks damaging the EGT probes, wires and hoses routed near the oil filter makes it difficult to replace etc.

As other have pointed out, a service loop hidden behind the instrument panel for future repairs, and minimum wires in the engine compartment are more traditional.

Clarence

[Vance Harral]

Because the input impedance (usually 50mega ohm range) is so high there is no measurable voltage drop along the wires.

 

True of all modern thermocouple instrument designs, including every all-cylinder engine monitor on the market today.  But some ancient instruments employ a needle movement which depends on current driven through the wires by virtue of the voltage induced at the thermocouple junction.  On those designs, the length of the wire matters, because the needle movement is calibrated for a specific current bias based on the resistance of the total wire length.  I've never seen such an instrument in person, even on some pretty old airplanes.  But they did exist, and are the source of the admonition not to cut thermocouple wires.  It's possible your helper is confused about this, but more likely he was just trying to save time.  A lot of engine monitor packages are sold with the probes pre-wired, i.e. they already have connectors soldered at all the interfaces when they come out of the package.  Shortening the probe wires in this case requires splices and/or resoldering the connectors.  It's easier to just tie up the excess where convenient, and call it a "service loop".

[carusoam]

Vance,

In the situation where the EGT is powered by the voltage difference of the probe (my old C)...the gauge is not calibrated.

It is easily adjusted so that Peak happens at the same place and the lines are in°F.

Tommy,

Cutting the wires is not recommended. (Requires specific knowledge on how to handle this) probably cutting at the end nearest the electronics is best. No soldering or welding of the wire is allowed...cutting out the middle won't work...

Hiding the extra length behind the IP is good.

Nylon ties have been known to cut through aluminum tubes. What are the intake tubes made of?

Check for other nylon ties that may have contact with fuel lines or oil lines. Special clamps with a softer plastic or rubber are popular for this.

As usual, I am not a mechanic. Just a PP....

Best regards,

-a-

[RobertGary1]

If there is vibration that zip tie will eventually wear a hole in the stack. That's why Adels exist.

 

-Robert

[N601RX]

Jpi pre attaches the db25 connectors on the monitor end of the harness, but does not crimp the ring terminals or other connectors on the engine end of the harness.  If they put them on for you it would take a huge hole to get them through the firewall. You can cut whatever length is necessary off the engine end of the harness before crimping the connectors on.