Tachometer Generator Aircraft
Kayleen
So, how does it work? The AC generator tachometer consists of a permanent magnet that is rotated inside stator windings wound in a three-phase star configuration. Three stator outputs are connected to the stator windings of the motor. As the engine turns, the permanent magnet induces currents in the stator windings. The three-phase output induces a rotating field in the motor stator windings.
Thank you very much for the information. As you said, if I was to buy the part from Cirrus, I need to use your part number (12323-001). Just managed to get a price from TC Aviation (Nearly $700) I have a Cirrus engineer coming to have a look at the unit/wiring this Friday. Hopefully he will be able to work out the source of the problem.
By the way our problem is this: when the aircraft is started from cold, the indication will stay on zero, after a few minutes it fluctuates between its real value and zero, and when in flight (cruise) it behaves normally, including after landing taxiing etc. When the engine is shut down and restarted, the problem also restarts itself !!
I had a bad experience with an overhauled MCU purchased by the maintenance company last year. 2 or 3 of the current sensors inside the MCU had to be replaced. Which actually took a number of visits and test flights to find the offending components as they were intermittent. I still get glitches from time to time with ALT-1 or ALT-2 light coming on.
I guess Cirrus will need to find a way to have a better control over the quality of parts they are buying in. There is just far too many electrical problems. At the same time, the only way that I can see might help to improve the reliability of the parts supplied, is complains raised by the inflicted customers.
I had one of the unit taken a part, and shockingly witness the poor quality and cheapness of the unit and the way it was put together. I am not surprised the unit fails after so many hours. In our aircraft it was replaced in late 2011 and the unit has lasted about 400 hours. The main component in the unit is a position sensor made by Honewell and retails around $15 (517SS16).
**I can also tell you I have seen bicycle speedo with better quality and reliability than this Tacho Sensor. **Once again, it proves the point that, some manufacturers perceive the aircraft owners to be nice and generous, whom are generally prepared to pay whatever price they ask for and easy to be taken for a ride.
There is two different tach generators with the same part number. The original had a very thin shaft that wore out very quickly. The 2nd generation, per say, has a more robust shaft and lasts quite a bit longer. When ordering make sure that you ask for the latest version. I found out the hard way that there are quite a few of the originals still out there.
I am not just sure as the type of approach Cirrus could take to find a replacement. The problem is the SR20 market is quite small so the development cost could become an issue, although selling a product that can cost no more than $30 to produce for $700 should be a good tempter and certainly help the cause.
Attached to the aircraft engine or rotor machine shaft is an armature. One end of this armature rotates within the magnetic field created by the tach generator. As the engine or rotor RPM increases, the voltage frequency created by the rotating armature increases at a proportional rate. This voltage is measured by a voltmeter circuit, which translates that voltage reading into a matching speed value displayed on the tachometer.
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On a flight to Little Rock today I noticed my tach bouncing up and down about 100 RPM. The engine was smooth so I think it may be an issue with the cable. Have any of you guys had an issue with this and what was the solution? I've heard lubing the cable can help.
I have an acquaintance that had this occur. It wobbled (about 100 RPM back and forth) even without engine vibration. He was annoyed by this and his choice was to overhaul the tach or replace it. You can buy a new tach (and have the hours set to be the same) or look at some aftermarket products. He ended up buying the EI tach and really likes it. Looks cool too...
I had the same condition for a 100 hours or so. One day, about 2 months ago, I was flying along minding my own business and the most god-awful shrieking CAUGHT MY ATTENTION. My tach was pinned, and then to zero, pinned again with awful screehing, and then zero, and then dead tach. I have an electronic tach which of course remained steady the whole time.
I had that happed to my 93 with an electrical tach generator. Finally the cable broke. I replaced it with a new cable. That lasted less than 1 year and it too broke. I got a new cable from Mooney and that was manufactured incorrectly. Mooney said it would take months before the vendor could replace the defective cables. They suggested I try attaching the tach generator directly to the engine where the cable used to go. It was a very tight fit, but I got it to work. It's been 2 years and the tach has worked great.
yeah i have this issue in my 61B. I live with it for now and just read the average of the bouncing. I'm pretty good at it now haha. I will get it lubed up when i get the annual tho since its coming up before long
I had my cable replaced at annual and it still has a little bounce to it, though not as bad as before. I am going to take the plunge and go with the digital tach that Horizon makes. Any reviews on this product?
Call me old fashioned but I still like analog guages and I recently purchased an analog UMA electronic analog tachometer because my cable driven tach was bouncing too. I prefer the analog because I can just glance at it and see if the engine RPMs are where it's supposed to be. Very easy to install; just remove the old tach with cable, install the new tach to power supply and route the electronic cable to where the old tach was connected. Install the tach sending unit where the old cable connected to the engine and that's it.
It consists of one stator with 3 phases 2 poles windings and a permanent magnet rotor. By turning the rotor, a current is induced in the windings of the stator with a frequency of one cycle per revolution of the generator shaft. It is designed for use with percent RPM indicators in turbo-jet engines. It can be employed up to 5000 RPM in either rotation direction when mounted in any position.
Aerosystems Tachometer Generators are housed in aluminium case Black Hard Anodized in accordance with MIL-A-8625. Alnico permanent magnets are used. Shafts are stainless steel, and rotate on shielded stainless steel ball bearings. The entire armature is impregnated.
Tachometer generators are special direct current generators that produce a very linear voltage per rotation speed. The linearity accuracy may deviate at ultra-low speed or at speeds beyond the tach-generators maximum recommended speed. This allows a remote voltage meter to be calibrated to the tachometer generator and indicate tach-generator speed (RPM) or speed of any device/apparatus coupled to the tach-generator.
Tachometer generators are frequently used to measure engine and motor speed, as well as the corresponding speed of powered equipment such as conveyors, mixers, fans, and machine tools. They are therefore employed as feedback components in speed control circuits.
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The Model 3800 is a compact, lightweight and quiet tachometer tester designed specifically for calibrating and troubleshooting aircraft and helicopter tachometer indicators and generator/alternator systems on the flight line and in the workshop. The Model 3800 exceeds current U.S. Navy specifications.
Calibration can be performed in the clockwise or counter-clockwise directions using RPM units, or as a percentage of full scale from 1% to 120 % (42 to 5040 RPM) in 1% increments for jet engine tachometers.
Needle fluctuations and erratic readings are quickly isolated using the manual Adjust mode. The AND 20005 drive pad allows the unit to be used with all standard aircraft tachometer generators and alternators.
A standard SAE cable adapter is included with the test set for convenient testing of cable-driven tachometers. Internal switch-selectable Wye-connected and delta-connected load banks are also included to facilitate voltage output testing of phase tachometer generators under load.
Calibrates 2 and 4-pole generators, as well as RPM and % indicators.
Calibrates optical tachometers from 500 to 65,000 ROM with the (optional) optical tachometer kit.
Calibrates jet engine tachometers as percentage of full scale from 1% to 120%.
Calibrates electrical and cable-driven tachometers.
Accurate to within 0.02% of set point value.
Normal operating range from 1 to 6,500 RPM.
Intuitive front panel controls for efficient testing.
Manual Adjust mode for easy tachometer troubleshooting.
Standard AND 20005 drive pad.
Internal Wye-connected and delta-connected load banks.
Quiet operation.
Stores up to 4 user-programmable test scenarios for both Tacho-Gen and Tacho-Indicator (in addition to the standard scenario).
Intuitive controls shorten learning curve for inexperienced operators
Target speeds and System status information easily available on vacuum fluorescent front panel display
Includes standard SAE cable adapter for testing of cable driven tachometers. Also included are internal switch-selectable Wye-connect and delta-connectable load banks are also included.