Westach 712-912K CHT thermocouple

[A321Flyer]

I just replaced the original CHT-senders with Westach 712-912K J-thermocouples. 2 questions:

- I need to extend the wires by about 15 inches (already behind the firewall). Do I need to be careful about what kind of wire I am using for this extension?
- The wiring goes to CHT1 and CHT2. How about polarity of the J-thermocouples? The Westach comes with a white and a black cable. Which one goes to which input?

Thx, Martin

 

[dynonsupport]

You want to use J-type thermocouple wire for any extensions you make. We sell it for a buck a foot.

Can't say for sure on the wire color conversion. We use standard thermocouple wire, where for type J, white is considered + and red -. Also, white is an iron (magnetic) wire, while the red is copper/nickel and is non-magnetic, if that helps. You might ask Westach to be sure.

 

[A321Flyer]

Thank you for the info.

I do have some wire left, which came off the wiring harness from Stein for the EGT (brown isolation, red/white wire). Can I use this for an extension of the CHT-wiring (i.e. your Rotax-EGT-sender is also a J-type thermocouple)?

I will ask Westach about the polarity of their sender.

Martin

 

[A321Flyer]

Some information about the 712-912K-sensor (email from Westach):

****
HI Martin
The white is pos and the black is neg. You can remove our connectors with a little heat from a solder iron and install your own connectors.

Thank you
Pete
Westach / Westberg Mfg Inc
www.westach.com
****

 

[A321Flyer]

Problem connecting J-type cable

Hi Dynon-Support

I just installed the longer J-type cable to the Westach CHT sensors. I made the connection using a crimp contact. Problem now: If I heat the connection with my hand, the temnperature indication drops immediately by 10-15° C.

Obviously my connection technique (crimp) is not good...

Do I have to solder it? What is the correct technique to connect J-type cable?

Thx and best regards
Martin

 

[Dynon]

So, when you have a thermocouple junction, you ideally want to use a connector made out of thermocouple material. If you don't (many people don't), then, if there's a temperature change across the junction (as you're probably inducing with your hand), you'll see some temperature error in the reading. If the entire junction plus both sides of the wire are being heated and cooled uniformly, even when you don't use thermocouple material in your junction, then you won't see that temperature change.

So the rules of thumb are:
-For ideal performance, use thermocouple-specific junctions (for the specific type of wire)
-Most people don't do this, but that's only OK if there's no temperature change across the thermocouple junction.
-Your test likely induced such an uneven change across the junction, which would show such an error.

 

[A321Flyer]

Thank you for the info! Now I understand.

I was somewhat surprised that the temperature error was that significant when heating the junction with my hand (though both cables were heated), but true, this is a very sensitive measurement.

I will try first to isolate the junction thermically (it is on the cockpit side of the FW). Like that I whouldn't have quick changes in temperature on the junctions (e.g. when opening the cabin heat or air vents) and the error should be smaller. If that still doesn't work, I consider installing J-type connectors (although they are somewhat hard to get here in Switzerland).

Thx again, Martin

 

[A321Flyer]

High reading of Westach 712-912K CHT thermocouples

I am still having troubles with the Westach CHT sensor: The reading of both CHT sensors is 17°C high (compared to 2 EGT, Dynon EFIS-T-Sensor and bulb thermometer in the workshop).

I use J-type extension wire (junction for the extension is not J-type yet). However all wires, junctions, aircraft parts are at the same temperature (room temperature which is +5°C in my workshop), so I really wouldn't expect any discrepancy in the CHT reading...

How comes? Do you have any ideas? This needs to be definitely fixed before I start the engine.

Thx Martin

 

[A321Flyer]

Amendment:
When switching on the EMS, all 4 engine sensors (2 EGT, 2 CHT) show similar values (today: between +4 .. +6°C). While working in the workshop, the temperature rises slighty to approx. 8°C (within 1 hour), which is displayed correctly by the 2 EGT sensors. The CHT sensors however display a temperature of approx. +25°C then, which definitely is wrong.

Any ideas?

Thx Martin

 

[Dynon]

A J thermocouple is a J thermocouple, as far as SkyView is concerned. So as long as that's the thermocouple type, it should work, provided it's not hooked up in reverse. A couple of things to try:

What direction does the probe go when heated (heat it with a lighter or a hair dryer or something)?
When not grounded to the engine (with the probe in free air), does anything change?
Are you sure you've got type J selected for those pins in the pin mapping section of the EMS setup?

 

[A321Flyer]

Problem is still not resolved...

- When the probe is heated (hand/fingers around the probe head), the CHT-temperature indication is increasing accordingly.
- When the probe is in free air, it still gives the same wrong reading (20°C high).
- I have the CHT connected to the EMS120, so I think there is no pin mapping section available?

I don't understand at all why the reading is correct initially when switching on Master Switch and EMS, but after approx. 1/2 h the reading of both CHTs is +20°C high (and stays there). If I switch off elec power and switch it on again, the reading is still 20°C high then.

Could it be that there is a temperature rise in the connector to the Dynon EMS-120 that causes the error? There is nothing else along the entire sensor cable and sensor that changes over time.

I have no idea of what else to try...

Is there a certain setting in the EMS that I have to use? Setup is set to Rotax Engine, 2 CHT, 2 EGT. The 2 GPs are used for two additional fuel tanks.

Thx and regards
Martin

 

[A321Flyer]

I did some more „testing“ today:
A. Checked voltage at cable ends (at pins of D-Sub-Dynon contactor, disconnected from Dynon EMS)
- before switching on Dynon EMS: 0.0 mV (T-Indication on Dynon = 18°C for both CHTs which equals room temperature)
- after 1 hour: approx. 0.5 mV (T-Indication on Dynon = 39°C for both CHTs, room temperature however still 20°C)

B. Checked voltage at junction between thermocouple cable and thermocouple extension wire after 1 hour (when CHT reading is already 20°C high):
- voltage at junction: 0.0 mV
- voltage at connector to Dynon EMS: 0.5 mV

It seems like as the problem might be caused by the extension wire?! It is J-type shielded extension wire, black cable connected to black cable of Westach CHT probe (and white to white). I connected the extension wire of one CHT probe with crimps and of the other CHT by soldering. As the result is same for both CHT, I suppose that the problem is not related to the way I connected the extension wire but to the extension wire itself?

I still don’t understand why the reading is ok when switching on the Dynon but changes to a 20C high reading within 1 hour of Dynon EMS operation…

Hope I can fix this thing – it starts driving me crazy …

 

[A321Flyer]

J-type color coding different US <-> International

Problem solved!

The international and US color coding for J-type extension wires is inverted (http://thermocoupleinfo.com/images/color-codes.jpg).

Westach (US) cabling is: WHITE = pos. / BLACK (or RED) = neg.
International cabling is: BLACK = pos. / WHITE = neg.

After having changed the cabling, everything works fine!

Wow, this took me quite a while to figure out...

Thx for your excellent support and regards
Martin