Tach update for GMCTD

[mhagie]

jd, Still unable to run my truck as it has issues w/injectors on my D.D. reman,it accidently ended up w/reman injectors of which a couple are a little suspect,NEW ones are on the way.
In the meantime since I have a stub ess that came w/reman I decided to clamp it in vice hook up the tach/breadboard assy and see what happens when running it with my cordless drill.
AHAA, it works but will only obtain a max reading of 500RPM with drill maxed out at 1450 rpm which should have been a reading of 2900 tach RPM. :confused: but at least its a start in the right direction.
Did a ohm check on stub ess =1209 ohms,checked ess in truck 0 ohms, WHOA something wrong here turns out the lead to chassis ground wasn't. so removed it, will run it into cab and do it right connecting it at the circut and tach grounds.
Checked truck ess again =1205 ohm, much better.
Any guess as to why the rpm so far off?
Scope not here yet so can't play w/it.
Thanks in advance.............Merle

[gmctd]

You can verify signals with the scope - not enough amplitude can cause that symptom.

Dr Lee indicated some type of adjustment for accurizing, but that's usually somewhere around +/- 5%.

Just have to wait and see.

By the way, good idea for testing the setup.

jd

[mhagie]

jd, e-bay scope arrived sat pm it is a older heathkit general purpose scope it has a small screen w/2"x2" square checkerboard 8 sq vert & 8 horiz w/hash marks centered vert&horiz,other than that it is blank.
I can hook up the vert input and spin ess and get a sawtooth pattern but there is nothing on scope that I can apply a numeric value to. the pattern is affected by the adjustment of either the hor or vert amplitude knob or the freq vernier knob.
In laymans terms I don't know what the h&#l I'm doing, I got scope cheap, methinks I may have pulled a boner here?.
Don't most modern scopes have numeric values on the vert& hor side of screen?
Dr. Lee mentioned that he adj trim pot to match tach to scopes 4pulses in 25 milliseconds,I question if my scope has that capability.
If you care to post e-mail address I will send pics I don't know how to attatch pics here.
I'm starting to get a little discouraged here but don't want to give up as I like the design if I can only make it work.
Next dumb question what componet in this circut increases amplitude?
Last question is just what design of scope do I need here so I know what to look for?
Sorry for all the stupid questions but desperation does that to a fellow. :D
Thanks again ............Merle

[gmctd]

The pattern on the screen is in square divisions

Vertical measurement (amplitude) is VOLTS per division
The Vertical Input switch is scaled in Volts/Div
Set switch to 1v, each vertical square represents 1 volt
Setting the trace on the center 'hash' to represent zero volts, the screen will display 4 volts up (+) from center and 4 volts down (-) from center for 8 volts peak to peak ac
Set the trace on the bottom division, the screen will display +8 volts dc level

Horizontal is TIME per division, in seconds
The Sweep Time switch is scaled in Time/Div
Set the Sweep switch to 1ms, each horizontal square represents one millisecond.
Set the switch to 5ms/div, 5 divisions are 25ms, full screen 8 divisions would be 40ms total, so you would see four pulses per 25ms, for 2400rpm.

Dr. Lee saw 4p\25ms - there are 40 25ms periods in one second, which would be 160 pulses per second.
2400rpm divided by 60 seconds is 40 rotations per second times 4 ESS pulses gives 160 pulses per second.

2900rpm is 48.33 rotations per second times 4 ESS pulses gives 193.33 pulses per second, so you would see 5 pulses in a little more than 25ms (193.33 divided by 40 (25ms) periods = 4.8)

Module output amplitude is set by supply voltage on the 1k pullup resistor and the tach's input impedance.
Base biasing and transistor hfe can effect turn-on/turn-off levels, limiting amplitude

That scope should do what you need of it.

jd

[mhagie]

jd, My apologies I forgot to mention in previous post that it has a Hor./Freq selector knob.
Its settings are, Hor.in/line sweep/20/200/2kc/20kc/100kc
The vert and hor amplitude knobs have no numeric values just 9 evenly spaced dots around the knob.
There is also vert and hor centering knobs that appear to be used to control vert centering and width of line,I now believe that they represent something but not sure what.
What is the function of the Freq/vernier control
I know that when you turn on unit,center the line w/vert amp adj hor amp to width of squares the line is pulsating/vibrating if you will,by turning the vernier control it becomes a solid and stable line.
The book is quite vauge as to control functions as I supose that they never took into consideration that it would be in the hands of a nimrod.
Your help in this matter is appreciated, I am slowly catching on as you explain things.
Many many thanks........Merle

[gmctd]

Ok - I needs to rescind a statement :
I do not now believe that scope will be suitable for all your needs.
We can get by for basic testing the module, but that's a free-running scope, not a triggered version, as I first assumed.
Many of us older hands learned basic electronics on just such a scope, made by Dumont, and thought it to be the most wonderful piece of equipment we'd ever seen. Dumont also starred in many an old sci-fi movie, including 'TRON.

Measure a flashlight battery, set the Vertical knob to a dot which gives you 1 1/2 vertical divisions - that should be the 1v/div range. It usually runs in a 1 - 2 - 5 sequence.
The vertical vernier enables a calibration adjustment to a known value. Adjust the vernier to give exactly 1 1/2 divisions, the 1 volt range is calibrated.
On the 2 volt range, 6 1/4 vertical divisions is 12.6v.

Same with the Horizontal Freq adj., which is 1/t
20 = 50ms (milliseconds)
200 = 5ms
2kc = 500us (microseconds)
20kc = 50us
100kc = 10us

Each range can be calibrated to a known frequency standard with the vernier knob.
-Or-
You could hook the ESS test 'stub' to a 1/4 hp or so ac induction motor, at 1725 rpm. 60hz ac is fairly stable, so you'll get an accurate 1725rpm for 3450rpm tach calibration.
-Or-
You could get a 115v to 6v transformer, connect 6vac\60hz to the module input and set the tach for 900 rpm.
2400/160=15 x60 =900
Some cordless phone sets use 6v to 9v ac transformers.