Author Topic: Engine tachometer (rev counter)  (Read 4993 times)

0 Members and 1 Guest are viewing this topic.

Offline Paul C

  • Regular User
  • *****
  • Posts: 78
    • View Profile
Engine tachometer (rev counter)
« on: July 26, 2012, 12:07:14 PM »
Many years ago I purchased, among some other small bits 'n' bobs, an engine rev counter purportedly from XL427.

I'm interested in knowing a bit more about how it works - I did have a post on the 'old' forum but I can't find it now.

The info on the back of the unit is as follows:

Indicator Tachometer Mark II Type 3D 160
Ref No. 6A/3251
Ser. No. 5019/61
Mod No. A.40001
Elliott Bros. (London) Ltd
 
There is a screw-in connector on the back in which are 3 pins, so my first question is - is it mechanical or electrical?
« Last Edit: January 01, 1970, 01:00:00 AM by Guest »
Vulcan - Filling the sky with sound since 1952...

Offline Oberon

  • Vulcan Engineer
  • Regular User
  • *****
  • Posts: 110
    • View Profile
Re: Engine tachometer (rev counter)
« Reply #1 on: July 26, 2012, 01:52:14 PM »
Here's an explanation I prepared earlier:

Each engine has an Elliot Mk 11 tacho generator fitted which develops 3Ø ac at a frequency proportional to engine speed. The indicators are of a synchronous motor type which drives a pointer mechanism through a magnetic drag assembly.  At maximum engine speed, the tacho generator runs at 4200 RPM, which gives an indication of 100% on the indicator. On bench tests, values of percentage indication for specified RPM are shown below.

Test Bench          Percentage
Speed (RPM)      Indication

800                      19.05
1000                      23.81
1500                    35.72
2000                      47.62
2500                      59.55
3000                      71.44
3500                      83.35
4000                      95.26
4200                      100.00


The resistance between the terminals of the tacho generator is 25 ± 5 ohms and the measured value of each phase is within 1 ohm of the others.  
For some reason I can't get the Percentage Indication figures to line up (on preview) but 800 RPM is 19.05%

Hope this Helps   :)

Oberon
« Last Edit: January 01, 1970, 01:00:00 AM by Guest »

Offline Paul C

  • Regular User
  • *****
  • Posts: 78
    • View Profile
Re: Engine tachometer (rev counter)
« Reply #2 on: July 26, 2012, 02:06:15 PM »
Quote from: "Oberon"

Hope this Helps   :)

Oberon

Wow, yes that's really interesting thank-you. And there was me hoping to connect a car battery to see if it works, but my feeble grasp of all things electrickery-related would probably let me down and result in a broken gauge!

Thanks for your response.
« Last Edit: January 01, 1970, 01:00:00 AM by Guest »
Vulcan - Filling the sky with sound since 1952...

Offline vulcanfreak

  • Club Member
  • phpBB Newbie
  • *****
  • Posts: 34
    • View Profile
Re: Engine tachometer (rev counter)
« Reply #3 on: July 27, 2012, 08:24:02 PM »
XL427, a good friend of mine dismantled this aircraft (after being blown up!) and he still has 2 1/2 of its engines in his garden!
« Last Edit: January 01, 1970, 01:00:00 AM by Guest »