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Garmin GTX330 altitude encoder

There are some matters in that video which are referenced here. I will cross-post it there.

Administrator
Shoreham EGKA, United Kingdom

@Ultranomad and @NCYankee thank you

Meanwhile this interesting YouTube came up



Oxford (EGTK), United Kingdom

Ultranomad wrote:

I can’t vouch for all encoders, but here is an excerpt from the service manual for ACK A-30, a fairly popular type. You obviously need a pitot-static test set for that.

Thanks a lot!

EGTR

@arj1, I can’t vouch for all encoders, but here is an excerpt from the service manual for ACK A-30, a fairly popular type. You obviously need a pitot-static test set for that.

1. Calibration should be done with both the primary flight altimeter and Digitizer at the same ambient temperature within the range of +55 to +95°F (+15 to +35°C). Power supplied to the Digitizer should be of the same nominal voltage as the aircraft buss voltage to which it is to be installed. The digitizers are factory calibrated at 14V nominal voltage, when calibrating using 24V buss voltage the factory calibration will be 100-200 feet off at sea level.
2. Apply power to the Digitizer for at least 5 minutes before proceeding with the calibration.
3. Determine the altitude to which you will be calibrating the encoder. Supplied with the Digitizer are four (4) altimeter placards. (See figure 5)
4. With the primary flight altimeter set to 29.92 in Hg, decrease the system pressure supplied by the pitot –static test set until the primary flight altimeter indicates 50 feet lower than the maximum altitude to which you are calibrating.
5. Check the code transition point at this altitude and if required adjust the trim pot marked “H” until the transition point is within ±50 feet of the primary flight altimeter with both increasing and decreasing pressure.
6. Increase system pressure until the primary flight altimeter indicates +50 feet. If required adjust the trim pot marked “L” until the transition point is within 10 feet of this altitude with both increasing and decreasing pressure.
7. Repeat steps 4 through 6 until an accuracy of ±50 feet is obtained for both increasing and decreasing pressure at both maximum calibration altitude and 0 foot altitude.
8. Install a placard which corresponds to the maximum altitude to which the Digitizer was calibrated on the front center face of the primary flight altimeter.

LKBU (near Prague), Czech Republic

Ultranomad wrote:

RobertL18C, you don’t necessarily need a replacement, most encoders can be easily recalibrated.
It also makes sense to check whether the static pressure tubing is intact – if it’s broken, the encoder will show the cabin pressure altitude, which is slightly different from the one at the static port.

@Ultranomad, what is the procedure to recalibrate? How complex is that?
Thanks a lot!

EGTR

RobertL18C wrote:

Garmin appears to supply this unit

https://www.gps.co.uk/product/garmin-gae12-altitude-encoder-for-gtx3x5-011-03080-00/

I will check next week but suspect the engineers may have found an old encoder for the old Narco unit, which in the tradition of some installations had not been removed when the GTX330 was installed.

The encoder for the GTX 345 is not intended for the GTX 330. Any parallel or serial encoder will work with the GTX 330.

KUZA, United States

@RobertL18C, you don’t necessarily need a replacement, most encoders can be easily recalibrated.
It also makes sense to check whether the static pressure tubing is intact – if it’s broken, the encoder will show the cabin pressure altitude, which is slightly different from the one at the static port.

LKBU (near Prague), Czech Republic

My GTX330 is fed from a KEA130A encoding altimeter. Same unit driving the KFC225 and the TAS605.

Administrator
Shoreham EGKA, United Kingdom

Garmin appears to supply this unit

https://www.gps.co.uk/product/garmin-gae12-altitude-encoder-for-gtx3x5-011-03080-00/

I will check next week but suspect the engineers may have found an old encoder for the old Narco unit, which in the tradition of some installations had not been removed when the GTX330 was installed.

Oxford (EGTK), United Kingdom

There is no typical encoder for the GTX330, the market is full of suitable digital units.

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