how to use labview to read an encoder using a multimeter?

[sitzikbs]

a. thanks.

b. the encoder has 1250 segments.its  supposed to rotate at maximum of 250 rpm. whats the sample rate required for that? 

c. how do i control the sample rate? all i have is a "read" function from keithley. it has a parameter called power line cycles is that the parameter i need to change? 

[Tushar_Jambhekar]

I would again recommend you not to use DMM for this application. Even though the logic all these posts talking about are fine enough as logic. you will get many surprises as you go along real world development.

also regarding sampling speed: the speed mentioned is the sampling rate of ADC. it DOES NOT mean that you can read those 2000 samples in your PC.

Also DMM is supposed to measure RMS, so as you increase the motor speed all those pulses will give one fairly constant value, you wont be getting any fluctuating values to apply threshold.

You CAN use spoon to tighten the screw, but WILL you USE IT?

however if you still want to use DMM you need to measure at least 5208 PPS at peak speed (1250*250/60)

[sitzikbs]

i guess you are right. I will use a different optic sensor to count the revolutions (one that generates a single pulse whenever a certain point is reached.

i have another questions - i cant find where i define in labview the number of samples per second for my DMM. i used the keithley driver functions. does anyone know how do i change it? 

[Zwired1]

I agree, in principle, that the DMM is the wrong tool for the job.  I understand, also, that sometimes you don't get to choose the tools you have available or you just want to try something for the sake of "personal enrichment". 

In the spirit of enabling you to do what you're trying to do and not worrying too much about it, here is the VI I attached previously but it is now saved for ver 8.2. You should be able to open it in 10, but I saved it for older than that so that oithers in similar (but older still) situations can use it.

[sitzikbs]

thanks, ill try it and see how it works out. its my last hope... 

[djs_at_eaton]

It's not your last hope.

You can "do" encoder position and speed faster and easier with a couple of counters on a DAQ card.  It will probably cost you less than the DMM you're trying to use.

[sitzikbs]

ok so after failing to do what i wanted with keithleys multimeter i found a tektronix dpo 2024 scope that might be able to do the jopb . 

does anyone happen to have a vi for this scope to read the encoder ?
thanks ,

[NIquist]

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@sitzikbs wrote:

ok so after failing to do what i wanted with keithleys multimeter i found a tektronix dpo 2024 scope that might be able to do the jopb . 

does anyone happen to have a vi for this scope to read the encoder ?
thanks ,

---

A VI for using a $3000 scope to do the job of a cheap DAQ or quadrature decoder chip???  Don't hold your breath...

You say you only need to count revolutions (and calc the RPMs), many encoders have an index pulse you could count (probably even with your PCs parallel port .  Otherwise you'll need something fast enough to count the 1250 cycles * 250 RPM = 312500 Hz (Samples/Second).  Really 625000 considering my namesake NYquist!

Trying to force dedicated benchtop equipment to do this isn't turning a screw with a spoon, it's more like hammering in a nail with a spoon!

EDIT:  BTW, if you really need help with reading this encoder (and not just having fun with LabVIEW and test equipment) post it's brand and model number...

[sitzikbs]

hey man, you dont have to be mean about it. 

im running this project with no budget and im using anything i can get my hands on without spending money (even if that means using expensive equipment just because its there).

helpfull ideas are more than welcom. 

yes, im new to all of this, but im trying my best here 😞 

As for the encoder model its Renco Encoder RHS15D.

i know that there is the index signal that i can count. ill try this first. 

[AnalogKid2DigitalMan]

The 2000 can measure frequency in the AC V mode. You may have to level shift your encoder signal so it has - and + polarity below and above 0V. From the manual:

Measuring frequency and period

The Model 2000 can make frequency measurements from 3Hz to 500kHz on voltage

ranges of 100mV, 1V, 10V, 100V, and 750V. Period measurements can be taken from 2μs

to 333ms on the same voltage ranges as the frequency.

The instrument uses the volts input terminals to measure frequency. The AC voltage

range can be changed with the RANGE and keys. The signal voltage must be greater

than 10% of the full-scale range.

CAUTION The voltage limit is subject to the 8

× 107V•Hz product.

Trigger level

Frequency and Period use a zero-crossing trigger, meaning that a count is taken when

the frequency crosses the zero level. The Model 2000 uses a reciprocal counting technique

to measure frequency and period. This method generates constant measurement resolution

for any input frequency. The multimeter’s AC voltage measurement section performs input

signal conditioning.

-AK2DM