Today's Message Index:
----------------------
1. 06:08 AM - Re: EFIS Erratic Temp Readings (Kelly McMullen)
2. 07:51 AM - Re: Poor Man's Battery Tester (cjfortin)
3. 08:12 AM - Galloping ammeter (Robert L. Nuckolls, III)
4. 08:27 AM - Re: Re: Poor Man's Battery Tester (Robert L. Nuckolls, III)
5. 08:38 AM - Re: EFIS Erratic Temp Readings (Robert L. Nuckolls, III)
6. 09:41 AM - Re: EFIS Erratic Temp Readings (Robert L. Nuckolls, III)
7. 12:14 PM - Re: EFIS Erratic Temp Readings (Dick Tasker)
8. 01:51 PM - Re: EFIS Erratic Temp Readings ()
9. 02:05 PM - Re: EFIS Erratic Temp Readings (Charlie England)
10. 06:14 PM - Re: Some Thoughts on Z101 (dj_theis)
11. 07:57 PM - Re: EFIS Erratic Temp Readings (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: EFIS Erratic Temp Readings |
Understand that both EGT and CHT are thermocouples that measure small
changes in resistance. If you have nothing connected the resistance can
float. If you have less than solid, airtight soldered, crimped or screw
connection, the resistance will float. I'd still put my money on
connections that are not airtight. I fought the same issue thinking I
had bad probes until I switched from spade connectors to the OLC-2
connectors. Temps are now rock solid. Same for fuel flow sensor. In fact
on fuel flow the connection improved enough I had to lower the K factor
between .5-1%. You can get all the connectors needed for $30 for a 6
cylinder or $20 for a 4 cylinder. AFAIK EI changed all of their
instruments to the OLC-2 connectors instead of spade connectors.
I seriously doubt you will see much improvement with shielding the whole
system.
On 2/1/2021 10:51 PM, mikepienaar09@gmail.com wrote:
> If I only have sensor connected temperature reading is different for
> each scan and varies by up to 150 degrees between max and min.
>
> If I connect more sensors readings become more and more erratic. Even if
> no sensors are connected ghost readings appear for cylinders not
> connected with the same reading for EGT and CHT. Ghost readings vary
> from between -50 to 800 degrees.
>
> Hope that helps
>
> *From:*owner-aeroelectric-list-server@matronics.com
> <owner-aeroelectric-list-server@matronics.com> *On Behalf Of *David Saylor
> *Sent:* February 1, 2021 7:10 PM
> *To:* aeroelectric-list <aeroelectric-list@matronics.com>
> *Subject:* Re: AeroElectric-List: EFIS Erratic Temp Readings
>
> I can't tell you how effective foil would be but maybe thegroup can
> help troubleshoot. Can you describe how it changes? Quickly, with
> large displacements, on/off, gradually, etc? Is it around the range you
> would expect? Is it a single cylinder measurement or similar behavior
> at different cylinders?
>
> --Dave
>
> On Mon, Feb 1, 2021 at 6:27 PM <mike@vision499.com
> <mailto:mike@vision499.com>> wrote:
>
> Hello
>
> I have an EFIS that has erratic temperature readings when the engine
> is running.
>
> Manufacturer has suggested that EMI interference introduced by the
> ignition system may be the culprit and has suggested shielding the
> leads with tin plated copper braid that is grounded. I am unable to
> locate copper braid near me and will have to wait for a delivery
> from Aircraft Spruce. Will wrapping the leads with aluminum foil
> replicate the shielding effect for test purposes.
>
> The EGT leads (clamp on probe type) are already covered with a
> braided covering, which I presume is Stainless Steel for physical
> protection, will this act as an EMI shield and if yes how do I
> ground it?
>
> Copper Braid is sold in 1/8, 1/4, and 3/8 nominal flat width, any
> guesses as to what size will accommodate k-type thermocouple leads.
>
> Thanks
>
Message 2
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| Subject: | Re: Poor Man's Battery Tester |
On the updated file shouldn't the one wall power lead go the first set of normally
open contacts on the relay?
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=500529#500529
Message 3
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| Subject: | Galloping ammeter |
>Follow-up:
>
> 1). No discrepancies (high resistances)
> found at Field switch or fuse (though AGC fuse and holder contacts
cleaned).
> 2). No discrepancies at the alternator
> field and B connections or with the capacitor (condenser) mounted there.
> 3). Little improvement with further flight
> time (resulting in higher battery SOC) - this
> behavior started after a period of no use during annual inspection.
The resistance values I cited are measured in tens of milliohms and
cannot
be observed with the legacy volt-ohmmeter.
> 4). Significant improvement from
> unplugging and reseating the connector at the
> voltage regulator. Next time the cowl is off I
> will perform a more comprehensive contact
> cleaning (tough to do properly through the oil door).
Aha! this is suggestive of exactly the phenomenon
I was describing. The act of re-seating a connection
effected a CHANGE in resistance at that joint on the
order of a milliohm or two.
>
>So now I am back to a simple dancing ammeter
>(with regular period between 1 and 2 Hz) that
>has been the norm for several years. The =9CAC
>component=9D as measured with my cheapie Digital
>voltmeter is under 0.5V and my panel lights are no-longer flickering.
>
>I=99m chalking this one up to a poor connection
>at the voltage regulator and returning the replacement alternator.
Good show. Try the experiment I suggested where
you wire a regulator right to the back of the
alternator thus eliminating all other ship's
wiring . . . see if the ammeter stabilizes.
I don't think I explained the 'resistance' thing
clearly enough. We're talking about the resistance
of wiring COMBINED with the resistance of EVERY
metal-metal joint in the field supply pathway.
Total pathway resistance from bus through circuit
breakers, connectors, switches and intermediate
accessories like ov sensor all add up to much less
than an ohm. When the aircraft is new, all those
joints are fresh and unaffected by the effects
of environment and age.
The attached drawing is an excerpt from a Cessna
drawing for alternator installation. I've counted
all the metal-to-metal joints which ADD to the
resistance of the wire (22AWG at 16 milliOhms
per foot) . . . all of which are in series with
the FIELD SUPPLY path of a 3-terminal voltage
regulator. This same pathway doubles as the
VOLTAGE SENSE lead for the regulator.
As long as that total resistance is low (factory
fresh), all is right with the universe. 30 year
old airplanes are another matter. The "galloping
ammeter" phenomenon manifests when total path
resistance rises above a threshold for regulation
stability. We might be talking about a few
hundred milliohms . . . a characteristic you
cannot detect/measure with your ohmmeter.
In some cases, replacing the split rocker switch
'cured' the problem . . . but it is only one of
many contributors to rise in path resistance.
In a relatively short period of time compared to
airplane age, the problem returns because rise
in path resistance has multiple contributors.
This is why I suggested the short-lead, test-regulator
experiment. It gets bypasses all ship's wiring and
accessories. It serves to confirm that root
cause galloping ammeter is too high resistance
in the field-supply/voltage-sense pathway.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 4
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| Subject: | Re: Poor Man's Battery Tester |
At 09:49 AM 2/2/2021, you wrote:
>
>On the updated file shouldn't the one wall power lead go the first
>set of normally open contacts on the relay?
>
Good eye . . . yes. Thank you. I've posted
the corrected drawing at:
https://tinyurl.com/y5urfyrr
I took a closer look at the COTS battery
LV shut-off controller. It has a lot of
promise. I note that they do not bring the
normally closed contact of the relay
out to a terminal. Depending on their
board layout, we have a 50-50 chance that
the after-test-charging mode can be
achieved by tacking the charger(+) feeder
to the bottom of the board.
I've ordered some samples of this product.
I'll publish a page 2 to the Poor Man's
Battery Tester when I've had a chance to
evaluate the critter more closely.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 5
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| Subject: | Re: EFIS Erratic Temp Readings |
At 08:07 AM 2/2/2021, you wrote:
>
>Understand that both EGT and CHT are thermocouples that measure
>small changes in resistance.
Actually very TINY changes in VOLTAGE generated
by the Seebeck effect . . . small temperature
dependent voltages generated at the junction
of dissimilar metals.
>I had bad probes until I switched from spade connectors to the OLC-2
>connectors.
>Temps are now rock solid.
Joint quality in thermocouple feeds
are important given the very tiny
voltages involved.
>I seriously doubt you will see much improvement with shielding the
>whole system.
Agreed, It is exceedingly rare that adding shields
fixes any problem in an instrumentation
system.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 6
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| Subject: | EFIS Erratic Temp Readings |
At 11:51 PM 2/1/2021, you wrote:
>If I only have sensor connected temperature reading is different for
>each scan and varies by up to 150 degrees between max and min.
Whoops . . . missed this out the gate. If the readings
are THAT erratic you may have something else going on.
Is this a new condition or did it crop up after a period
of normal ops?
Are the readings believable when the engine is not
running? Does turning the alternator on/off make
a difference?
Are your thermocouples on the engine electrically
isolated . . . i.e. not grounded to the engine?
Does the EFIS installation manual speak to the need
for 'isolated' thermocouples?
The gross excursions of reading sound more like
a ground loop issue as opposed to connector quality.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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| Subject: | Re: EFIS Erratic Temp Readings |
Actually, the voltage is not generated at the junction. It is effectively generated
along the whole length of a conductor due to the temperature difference between
the two ends. In fact, the only
reason we get any output to measure is that the two wires of a thermocouple are
chosen to have different Seebeck coefficients. See this article for more info
tinyurl.com/3njog7qv
Nonetheless, the junction, as well all connections from the point where the temperature
is to be measured to the device doing the measuring, is definitely important
since a bad connection there will
probably cause significant errors in the generated output.
Dick Tasker
Robert L. Nuckolls, III wrote:
> At 08:07 AM 2/2/2021, you wrote:
>>
>> Understand that both EGT and CHT are thermocouples that measure small changes
in resistance.
>
> Actually very TINY changes in VOLTAGE generated
> by the Seebeck effect . . . small temperature
> dependent voltages generated at the junction
> of dissimilar metals.
>
>> I had bad probes until I switched from spade connectors to the OLC-2 connectors.
>> Temps are now rock solid.
>
> Joint quality in thermocouple feeds
> are important given the very tiny
> voltages involved.
>
>> I seriously doubt you will see much improvement with shielding the whole system.
>
> Agreed, It is exceedingly rare that adding shields
> fixes any problem in an instrumentation
> system.
>
>
> Bob . . .
>
> Un impeachable logic: George Carlin asked, "If black boxes
> survive crashes, why don't they make the whole airplane
> out of that stuff?"
>
Message 8
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| Subject: | EFIS Erratic Temp Readings |
From: owner-aeroelectric-list-server@matronics.com
<owner-aeroelectric-list-server@matronics.com> On Behalf Of Robert L.
Nuckolls, III
Sent: February 2, 2021 8:48 AM
Subject: RE: AeroElectric-List: EFIS Erratic Temp Readings
At 11:51 PM 2/1/2021, you wrote:
If I only have sensor connected temperature reading is different for each
scan and varies by up to 150 degrees between max and min.
Whoops . . . missed this out the gate. If the readings
are THAT erratic you may have something else going on.
Is this a new condition or did it crop up after a period
of normal ops?
Aircraft has never flown, only noticed this while testing engine.
Are the readings believable when the engine is not
running? Does turning the alternator on/off make
a difference?
Readings seem stable and accurate when engine not running, will test this
again.
Will run to-morrow and then disconnect alternator
Are your thermocouples on the engine electrically
isolated . . . i.e. not grounded to the engine?
Not sure what this means
I have K Type bayonet EGT sensors that clamp onto Exhaust
and 1 yellow and 1 red wire that connects directly to MGL RDAC unit
CHT sensors are under plug with same wire setup
Does the EFIS installation manual speak to the need
for 'isolated' thermocouples?
Cannot find a reference for "isolated " thermocouples
The gross excursions of reading sound more like
a ground loop issue as opposed to connector quality.
I have taken a ground from the EFIS directly to the engine
block. The engine mounting bolt is grounded to battery and to the starter
motor
I have also tried it with the RDAC ground attached next to
the EGT sensor but this made no difference
None of the leads are joined, they go directly from the sensor to the MGL
RDAC unit
Mike
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
Message 9
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| Subject: | Re: EFIS Erratic Temp Readings |
snipped
>
> Cannot find a reference for isolated thermocouples
> snipped
>
> None of the leads are joined, they go directly from the sensor to the
> MGL RDAC unit
>
> Mike
>
Ask MGL which style (grounded or ungrounded) they require for their RDAC.
Ground issues might not be limited to the sensors; poor/inconsistent
ground reference could be related to the RDAC, or the EFIS, or ???.
Charlie
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Message 10
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| Subject: | Re: Some Thoughts on Z101 |
> Re brownout booster: I'm pondering a plan-d . . .
> or are we up to 'e'? There are dozens of suitable
> step up devices on the market but I have no knowledge
> of their 'spool up' times nor can I personally
> vouch for their specifications without putting
> the device under test on the bench and doing
> some measurements.
I purchased a couple of these a while back from Amazon.
https://www.amazon.com/ANMBEST-LTC1871-Converter-Adjustable-Voltmeter/dp/B08CMKGRZQ/ref=sr_1_1?dchild=1&keywords=ANMBEST+2PCS+LTC1871&qid=1612318310&s=electronics&sr=1-1
Adjustable output and alleged 6amp continuous output.
I ran a quick test with a bench supply (using a GRT Sport EX EFIS as the only load).
The GRT only draws about 0.5 amps so it's not much of a load but likely
all I might need.
I captured two waveforms. The first with simply turning off my very dated "BK
Precision, bench supply. Turning off the supply left the output voltage to decay
with the internal caps bleeding down. Hardly a simulation of an engine starting.
The second might be slightly closer to a cranking environment, where I rapidly
turned the voltage control knob down.
For what it's worth. I like the thought of using one that has a known design and
components, as Eric is suggesting. I'll continue to test this unit but who
knows how long it will last.
Dan Theis
--------
Scratch building Sonex #1362
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=500540#500540
Attachments:
http://forums.matronics.com//files/voltage_control_change_in_bench_supply_with_grt_sport_ex_192.pdf
http://forums.matronics.com//files/bench_supply_power_down_with_grt_sport_ex_205.pdf
Message 11
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| Subject: | Re: EFIS Erratic Temp Readings |
At 02:12 PM 2/2/2021, you wrote:
><dick@thetaskerfamily.com>
>
>Actually, the voltage is not generated at the junction. It is
>effectively generated along the whole length of a conductor due to
>the temperature difference between the two ends. In fact, the only
>reason we get any output to measure is that the two wires of a
>thermocouple are chosen to have different Seebeck coefficients.
Actually no. There are TWO junctions. One is
attached to the temperature of interest, the
second resides at some REFERENCE temperature.
WAaayyy back when, multiple thermocouples scattered
about a test airplane at Cessna were paired with
'reference' thermocouples immersed in an distilled
water ice bath (0 degrees C).
The real temperature of interest is deduced by
comparing the test thermocouple with the reference
thermocouple. Views -A- and -B- in this excerpt
from the 'Connection.
http://www.aeroelectric.com/articles/Thermocouple%20Junctions.pdf
The reference junction doesn't have to be an ice bath,
it can be part of the indicating instrument wherein
'reference' is cabin environment temperature . . . there
will be compensating thermistors in the instrument to
improve accuracy over a range of cabin environments.
Non-electronic thermocouple instruments of old actually
measured that difference voltage with meter movements that read
full scale with tens of millivolts applied. In these
cases, there was considerable current flowing in the
thermocouple leads compared to electronic displays.
Hence, thermocouple wire lengths and wire gages were
critical to accurate measurement.
Electronic displays don't need to draw current from
the thermocouples hence, wire length and gage
don't matter . . . there are no voltage drops in the
lead wires. JOINTS in those runs are critical
in that they need to occur in pairs so that potentially
parasitic junctions cancel each other out. See chapter
10 in the 'Connection.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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