Merkle-Korff Motor and Tachometer

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andrey8
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Merkle-Korff Motor and Tachometer

Post by andrey8 »

I just purchased a Merkle-Korff DC motor(EY series) from a surplus store. It looks like it has a tachometer or encoder attached to it.
Here is a picture and some specs:
http://65.61.11.207/productpages/eyqm63264.htm<p>I found the specs for the motor on the Merkle-Korff website http://www.merkle-korff.com/modeymatrix.htm , but couldn't find the specs for the tachometer. Has anyone used this type of a motor before? Can anyone suggest a spec sheet for the tachometer? Thanks.<p>[ November 06, 2003: Message edited by: andrey8 ]<p>[ November 06, 2003: Message edited by: andrey8 ]</p>
bwts
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Re: Merkle-Korff Motor and Tachometer

Post by bwts »

From their web site:<p>"TACHOMETERS AND ENCODERS
Magnetic Tachometers • 16 pole AC tachometers (8 cycles/revolution) are available with motor models EYQM and CYMM • Tach voltage: EYQM 1.8 vrms per 1000 rpm typical • Tach voltage: CYMM 3.3 vrms per 1000 rpm
typical • Addition of the tachometer will add approximately .50" (12.7 mm) to motor length on Model CYMM and up to .30" (7.6 mm) on Model EYQM"<p>http://www.merkle-korff.com/access.htm<p>B)<p>[ November 07, 2003: Message edited by: Mr Bwtz ]</p>
"Nothing is true, all is permitted" - Hassan i Sabbah
andrey8
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Re: Merkle-Korff Motor and Tachometer

Post by andrey8 »

Thanks for the reply. I saw those specs too, but that is not enough information. If you look at the picture, the motor has 4 leads. Two of the leads are red and black(I am assuming that these are the power and ground connections) and two of the leads are green and yellow. I need to know which of these leads is for the signal generated by the tach? Are both of them signal leads? Are the power and ground leads common to both the motor and the tach? Also I need to know what kind of a pulse is generated by the tach, a sine wave, a square wave? Is the signal conditioned with an internal Schmitt trigger?
hlreed
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Re: Merkle-Korff Motor and Tachometer

Post by hlreed »

I don't know the specs, but you probably have a motor running a generator. So you have voltage in to the motor and voltage out from the tach/generator.
Harold L. Reed
Microbes got brains
andrey8
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Re: Merkle-Korff Motor and Tachometer

Post by andrey8 »

Here is a reply that I received from a Merkle-Korff rep regarding this, if anyone is interested:<p>"The black and red leadwires are for the motor and the green and yellow leadwires are for the tachometer. The green and yellow leadwires are the signal wires. The tach output is 5.5VAC min at 3,000 rpm."
andrey8
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Re: Merkle-Korff Motor and Tachometer

Post by andrey8 »

Ok, I checked it with a scope. The tach outputs a saw-tooth wave. Now the question is how do I interpret that with my microcontroller? Should I go through the A-to-D converter? I am using an HC12 board, the DP256 version.
bwts
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Re: Merkle-Korff Motor and Tachometer

Post by bwts »

How does the output of the tach vary with the rpm?<p>Does the frequency change?<p>Does the peak to peak value change?<p>B)
"Nothing is true, all is permitted" - Hassan i Sabbah
hlreed
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Re: Merkle-Korff Motor and Tachometer

Post by hlreed »

The saw tooth counts up and rolls over.
count
0 0
1 2
2 4
3 0
4 2
0 4
1 0
2 2
3 4
4 0
0 2
And so on. If this is a voltage, you will need to run it through an ADC. From the ADC you can either differentiate it or count the 0's to relate it to motor speed. If you go this route you will need to digitize the motor control also with an H-Bridge or something.<p>If you are making a servo out of it it might be designed so that you can run it through a comparator that compares your saw tooth wave with the motor wave and feed the difference to the motor.<p>I any event, the feedback algebra is:
Motor = Tach - wanted speed
Harold L. Reed
Microbes got brains
andrey8
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Re: Merkle-Korff Motor and Tachometer

Post by andrey8 »

It looks like the frequency is changing. So maybe I need some sort of a frequency counter? But how would a frequency counter accept a saw-tooth wave? If I run the tach output through a Schmitt trigger, will that condition the signal into a square wave, and then input it into the frequency counter?<p>If you think that might work, can you suggest which frequency counter and which Schmitt trigger to use? (part #?)<p>Thanks to everyone for their input and assistance. It is very much appreciated.
bwts
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Re: Merkle-Korff Motor and Tachometer

Post by bwts »

Depends on how u want 2 control the motor, digitaly or analogly?<p>B)
"Nothing is true, all is permitted" - Hassan i Sabbah
andrey8
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Re: Merkle-Korff Motor and Tachometer

Post by andrey8 »

Ok double-checked the tach signal with a scope, and it looks like both the amplitude and the frequency vary with RPMs. It looks like the change in amplitude is a more accurate measure of RPMs, than the change in frequency. I need to take this signal and feed it into a microcontroller(HC12). How can I detect the change in amplitude by using the micro? Any suggestions?
bwts
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Re: Merkle-Korff Motor and Tachometer

Post by bwts »

Well I would:<p> rectify the signal to get a DC level
set up a ramp voltage starting at zero
set the clock runnning
loop: compare the ramp voltage with signal level
if = then take the clock value else loop
put clock value into processor
look up chart - clock against rpm
rest of program...............<p>of course there may well B an easier way to do this!<p> After thought - isnt this what an ADC does?<p>B)<p>[ November 14, 2003: Message edited by: Mr Bwtz ]</p>
"Nothing is true, all is permitted" - Hassan i Sabbah
andrey8
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Re: Merkle-Korff Motor and Tachometer

Post by andrey8 »

Mr. Bwtz, thanks a lot. That makes a lot of sense. I never thought about rectifying the AC voltage and feeding it into the ADC. Your assistance is greatly appreciated.
toejam
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Re: Merkle-Korff Motor and Tachometer

Post by toejam »

How about rectifying the voltage, dividing it with a 1 meg pot and feeding it to a comparator set to fire at the voltage generated by the rpm's of the tach? When the correct voltage is reached, the signal from the comp. could disconnect the current supply of the motor.
toejam
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Re: Merkle-Korff Motor and Tachometer

Post by toejam »

How about rectifying the voltage, dividing it with a 1 meg pot and feeding it to a comparator set to fire at the voltage generated by the rpm's of the tach? When the correct voltage is reached, the signal from the comp. could disconnect the current supply of the motor.
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