Want to get velocity with quadrature encoder

I can count and measure the displacement from the encoder signal with your quadrature encoder example file.
But, can you please advise me know how to implement to get velocity or RPM from that somewhat easily?
Thank you for your help.

Hey Encoder,
You can measure velocity by using a buffered, counting operation. With a buffered operation, the count is latched on the rising/falling edge of the gating signal. Therefore, if you provide a signal to the gate with a known frequency, you will be able to mathmatically determine the frequency of the signal connected to the source.
You can usually use another counter to provide a gating signal with a known frequency. There are example programs that illustrate how to do this.
DAQ-STC: Measuring the Frequency of a TTL Signal (Easy-Level VIs)
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3DD4756A4E034080020E74861&p_node=DZ52329&p_source=External
Measure a TTL frequency with DAQ-STC or NI-TIO in Visual Basic
http://si
ne.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3D7A756A4E034080020E74861&p_node=DZ52329&p_source=External
I hope this helps.
Regards,
Todd D.
NI Applications Engineer

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i'm presently trying to figure out if i can use the PCI-6025E Card to count up/down with a quadrature encoder with no additionnal hardware. I know my answer lies in a document called "Using Quadrature Encoders with E Series DAQ Boards document " but it is not presently available on the ni website.
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Hi,
Thanks for Ross's help.But I cannot differ 6601's x4 mode from other counter/timer counting mode. In measurement position, what difference between them. And I just want to know whether my application viable.
We are trying to measure position with 6601. The frequency of quadrature encoder is from 100Hz to 8MHz. Now, we connet the A,B and Z channel directly to counter . Using the example in CVI, we change the filter to 100ns and use x4 mode. It works perfect at low frequency.
The problem is when the frequency of encoder is higher than 2MHz, the accuracy decreases greatly. I'd like to know about following:
1.Can 6601 do the previous task enough? Or I must change to use 6602.
2.If
6601 is available, is there any way to increase measurement accuracy ?(in software or wire connection )

>jimmyjimmy2000
"Hi,
Thanks for Ross's help.But I cannot differ 6601's x4 mode from other counter/timer counting mode. In measurement position, what difference between them. And I just want to know whether my application viable.
>>mross>The application is viable. However, the use may be difficult.
>jimmyjimmy2000
We are trying to measure position with 6601. The frequency of quadrature encoder is from 100Hz to 8MHz. Now, we connet the A,B and Z channel directly to counter . Using the example in CVI, we change the filter to 100ns and use x4 mode. It works perfect at low frequency.
The problem is when the frequency of encoder is higher than 2MHz, the accuracy decreases greatly. I'd like to know about following:
1.Can 6601 do the previous task enough? Or I must change to use 6602.
>>mross>The 6601 is just as good as the 6602 at 2MHz. Therefore, a 6602 will have the same problem of inaccuracy.
>jimmyjimmy2000
2.If 6601 is available, is there any way to increase measurement accuracy ?(in software or wire connection )"
>>mross>Yes, in the wire connection you can make improvements.
6601 can count as fast as 20MHz (60MHz with prescaling). The signal is noisy (containing addtional, incorrect information).
You must use an oscillosope to look at the signal. Look at it when 6601 is counting correctly, and look at it when 6601 is "malfunctioning".
The counter will increment whenever the signal is high for more than 5 nanoseconds. The conditions for "High" and "Low" signals must be strictly met. If the signal is greater than 0.8V, the counter may increment. The signal must then drop below 2 Volts for a "Low" to be seen.
This sounds wrong, but is true. The counter is expecting TTL signal conditions (Transistor -Transistor Logic). This specification is very broad.
A "High" will absolutely be recognised if the signal is greater than 2.0V.
A "Low" will absolutely be recognised if the signal is less than 0.8 V.
However, the range from 0.8V to 2.0V is "undefined." This means the counter could increment at 0.8V. It has been my experience that National Instruments TTL will always see 0.8V as a "High." If your noise exceeds 0.8V you will never be able to count accurately.
The problem will be solved when your encoder signal is read cleanly by the 6601. This is why I gave you the URL for US Digital in the previous answer. The circuits they sell can help to clean up the counter signals. You will have to see what works best, since I don't exactly understnad you application. If the noise is very bad, you may wish to use the Encoder to Binary Number circuit. There will be no noise in the reading of a binary number. Since your encoder may run as fast as 8MHz, you must be sure the circuit you choose is also this fast.
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Field Wiring and Noise Considerations for Analog Signalsv
http://zone.ni.com/devzone/conceptd.nsf/webmain/01F147E156A1BE15862568650057DF15?opendocument
Follow these instructions very carefully.
Also, this book is helpful to explain noise and how one may reduce it.
From Amazon.com you can get Grounding and Shielding Techniques, by Ralph Morrison.
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Hi,
I am using DAQ 6062E, with BNC 2120. I have a quadrature encoder, and I need to get the position, and velocity. I have modified BNC2120_Quadrature_Encoder vi from NI. I can compute the velocity (delta position/time loop) easily, however this is not very accurate. I need to have a high accuracy velocity, and I think I have to use the second counter to measure the frequency of channel. However, I am not able to calculate the velocity with this method. I have attached my vi. I appreciate if somebody can help.
My encoder is connected to CTR Source 0 (PFI8), and UP_DOWN (P0.6)
I have connected CTR Source 0 (PFI8) to CTR 1 Gate (PFI4)
Thanks!
Attachments:
try encoder_with frequency.vi ‏58 KB

I get reasonably accurate velocity from quad encoders by connecting the source of my counter to the internal 20MHz clock then gating said
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where can I find any example for connecting Quadrature Encoders with M Series DAQ Boards ?
The only more or less suitable example I found in nimseries DDK, is
"Count pulses from an external source using an external signal to control
the count direction" (nimseries\Examples\gpctex2.cpp).
But this example is not working correctly with Quadrature Encoders
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what means enums
typedef enum {
       kG0_Up_DownHardware          = 2,
       kG0_Up_DownHardware_Gate     = 3,
} tG0_Up_Down;
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typedef enum {
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} tId;
in (nimseries\ChipObjects\tTIO.h) ?
What initalization procedure I need to work with Quadrature Encoders?
I have PCI-6259 DAQ device
and I'm writing programm under QNX6 operating system

Hello alexey_3269,
If you want to read a quadrature encoder start with gpctex1.cpp and follow the thread.
I give you my code:
BEGIN CODE
==========
boardGpct->G0_Mode.writeG0_Load_Source_Select(tTIO::tG0_Mode::kG0_Load_Source_SelectLoad_A);
boardGpct->G0_Load_A.writeRegister(InitialCount);
boardGpct->G0_Command.writeG0_Load(1);
boardGpct->G0_Load_B.writeRegister(0);
boardGpct->G0_Load_A.writeRegister(0);
boardGpct->G0_Input_Select.setG0_Source_Select(9); //see above for choices, PFI8=9, 100 kHZ=18
boardGpct->G0_Input_Select.setG0_Source_Polarity(1); //0=CCW, 1=CW
//If using 80 MHz timebase
boardGpct->G0_MSeries_Counting_Mode.writeG0_MSeries_Alternate_Synchronization(1);
boardGpct->G0_MSeries_Counting_Mode.setG0_MSeries_Encoder_Counting_Mode(3); //3 for X4 encoder counting
boardGpct->G0_MSeries_Counting_Mode.flush();
//Enable Input Pins
boardGpct->G0_MSeries_ABZ.setG0_A_Select(9); //PFI8=9,
boardGpct->G0_MSeries_ABZ.setG0_B_Select(21); //PFI10=21
boardGpct->G0_MSeries_ABZ.setG0_Z_Select(10); //PFI9=10
boardGpct->G0_MSeries_ABZ.flush();
boardGpct->G0_Mode.setG0_Gate_Polarity(1); //invert=1
boardGpct->G0_Mode.setG0_Output_Mode(tTIO::tG0_Mode::kG0_Output_ModePulse);
boardGpct->G0_Mode.setG0_Loading_On_Gate(tTIO::tG0_Mode::kG0_Loading_On_GateNo_Reload);
boardGpct->G0_Mode.setG0_Loading_On_TC(tTIO::tG0_Mode::kG0_Loading_On_TCRollover_On_TC);
boardGpct->G0_Mode.setG0_Gating_Mode(tTIO::tG0_Mode::kG0_Gating_ModeLevel_Gating); //kG0_Gating_ModeGating_Disabled
boardGpct->G0_Mode.setG0_Gate_On_Both_Edges(tTIO::tG0_Mode::kG0_Gate_On_Both_EdgesBoth_Edges_Disabled);
boardGpct->G0_Mode.setG0_Trigger_Mode_For_Edge_Gate(tTIO::tG0_Mode::kG0_Trigger_Mode_For_Edge_GateGate_Starts_TC_Stops);
boardGpct->G0_Mode.setG0_Stop_Mode(tTIO::tG0_Mode::kG0_Stop_ModeStop_On_Gate);
boardGpct->G0_Mode.setG0_Counting_Once(tTIO::tG0_Mode::kG0_Counting_OnceNo_HW_Disarm);
boardGpct->G0_Mode.setG0_Reload_Source_Switching(tTIO::tG0_Mode::kG0_Reload_Source_SwitchingAlternate);
boardGpct->G0_Mode.flush();
boardGpct->G0_Command.setG0_Up_Down(tTIO::tG0_Command::kG0_Up_DownHardware); //kG0_Up_DownSoftware_Down
boardGpct->G0_Command.setG0_Bank_Switch_Enable(tTIO::tG0_Command::kG0_Bank_Switch_EnableBank_X);
boardGpct->G0_Command.setG0_Bank_Switch_Mode(tTIO::tG0_Command::kG0_Bank_Switch_ModeGate);
boardGpct->G0_Command.flush();
boardGpct->Interrupt_G0_Enable.setG0_TC_Interrupt_Enable(0);
boardGpct->Interrupt_G0_Enable.setG0_Gate_Interrupt_Enable(0);
boardGpct->Interrupt_G0_Enable.flush();
END CODE
========
I hope this code is appropriate to you.
FV1234

Want to get velocity with quadrature encoder

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