Altitude encoder

I need a new encoder. I currently have a Trans-Cal D120-P2-T. I can get
an overhauled exchange for $230. Should I do that or just replace it with
a new ACK A-30 or Ameri-King AK-350? The Ameri-King is the cheapest at
$150. I believe both the ACK and Ameri-King use an oven to compensate for
temperature variations, while the Trans-Cal does not. Is it better to
have one with an oven or without? Is the Trans-Cal a better encoder
making it worth the extra money?

I think it was the Ameri-King AK-350 that I replaced for my Trans-Cal
when it went belly-up. You do have to wait for the encoder to out put a
signal. I first noticed this when my GPS messaged me that it had an
altitude fail. This occured for about 6 minutes. I called the avionics
shop and they explained the warmup that is required. Other than that it
does work fine. The GPS does require a valid encoder signal for IFR
operations.

Chad Lemmen wrote:

I need a new encoder. I currently have a Trans-Cal D120-P2-T. I can get
an overhauled exchange for $230. Should I do that or just replace it with
a new ACK A-30 or Ameri-King AK-350? The Ameri-King is the cheapest at
$150. I believe both the ACK and Ameri-King use an oven to compensate for
temperature variations, while the Trans-Cal does not. Is it better to
have one with an oven or without? Is the Trans-Cal a better encoder
making it worth the extra money?

Ross Richardson wrote:
I think it was the Ameri-King AK-350 that I replaced for my Trans-Cal
when it went belly-up. You do have to wait for the encoder to out put a
signal. I first noticed this when my GPS messaged me that it had an
altitude fail. This occured for about 6 minutes. I called the avionics
shop and they explained the warmup that is required. Other than that it
does work fine. The GPS does require a valid encoder signal for IFR
operations.

6 minutes! Thats a long warmup. Is that during the summer or winter?
I live in Michigan so it may take a while to warm up during the winter.


Chad Lemmen wrote:

I need a new encoder. I currently have a Trans-Cal D120-P2-T. I can get
an overhauled exchange for $230. Should I do that or just replace it with
a new ACK A-30 or Ameri-King AK-350? The Ameri-King is the cheapest at
$150. I believe both the ACK and Ameri-King use an oven to compensate for
temperature variations, while the Trans-Cal does not. Is it better to
have one with an oven or without? Is the Trans-Cal a better encoder
making it worth the extra money?

Winter as it is in Texas. By the time I let the engine warm up, taxi
out, and do run up, the Altitude Fail message is gone. Summer, its gone
a little faster.

Ross


6 minutes! Thats a long warmup. Is that during the summer or winter?
I live in Michigan so it may take a while to warm up during the winter.

Chad Lemmen wrote
I need a new encoder. I currently have a Trans-Cal D120-P2-T. I can get
an overhauled exchange for $230. Should I do that or just replace it with
a new ACK A-30 or Ameri-King AK-350? The Ameri-King is the cheapest at
$150. I believe both the ACK and Ameri-King use an oven to compensate for
temperature variations, while the Trans-Cal does not. Is it better to
have one with an oven or without? Is the Trans-Cal a better encoder
making it worth the extra money?

The Trans-Cal is not like the other encoders. It is built exactly
like an altimeter, bellows and all, but instead of a dial and hands it
has an optical encoder disk. The electronics are only used to change
the optical signals into electronic ones. No tuning, no drift - the
adjustments on a Trans-Cal are actually mechanical. What this means,
in practice, is that needing adjustment is VERY rare,

The ACK and Ameri-King are electronic beasts, they're analog, and they
drift. They tend to need adjustment every year or two, even with the
oven.

You can generally pick up a used Trans-Cal for about $100.

Michael

I talked with Trans-Cal and they said they would overhaul my D120-P2-T
encoder to like new with all the updates (mine was manufactured in 1974)
for $300 or they would exchange mine for the newer SSD-120-30 solid state
unit for $165. It seems like the easy decision would be to get the solid
state unit, but they did say that those units tend to need re-calibration
every two years and may need repair after 5 years or so. The older style
encoder will most likely last 30 years and may never need calibration. I
chose to get mine overhauled, I think it will save me money in the long
run. It sounds like the ACK and Ameri-King units also need calibration
often. I looked through my logs and can't find any entries for repairs to
my encoder, which means it has lasted 29 years.