Draw-Wire Sensor Guide

What Is a Draw-Wire Sensor?

Draw-wire encoder (ENC4118_0)

Draw-wire sensors provide an accurate and cost-effective method of measuring an object's linear position and/or speed.

As the draw-wire is pulled from the housing, a digital signal is generated which provides precise information about the length of the extended draw-wire.

Example - Length Measurement

The ENC4118 is used with an Quadrature Encoder Phidget and a VINT Hub Phidget (offscreen) to measure length. The results are displayed on a Graphic LCD Phidget

Which Draw-Wire Sensor Should I Use?

TODO: UPDATE THIS SECTION WHEN INDEX CHANNEL GUIDE IS AVAILABLE

Phidgets Inc. currently offers two types of draw-wire sensors:

Product ID		Draw-Wire Length	Resolution	Max Pull Speed	Max Wire Load	Index Signal
ENC4118_0		1m	10µm	300mm/s	500g	Yes
ENC4119_0		3m	20µm	300mm/s	500g	Yes

How Do I Get Data From My Draw-Wire Sensor?

All draw-wire sensors sold by Phidgets Inc. connect directly to our encoder interfaces.

For new designs, we recommend using the Quadrature Encoder Phidget - ENC1000_0 (pictured above). The Quadrature Encoder Phidget will monitor the output of the draw-wire sensor and update your software with an easy-to-use encoder count value.

There are also encoder interfaces built into many of our Motor Controllers. If your project includes a motor controller, the onboard encoder interface is a great option for our draw-wire sensors.

Converting Encoder Count to Length

TODO: UPDATE THIS SECTION WHEN SPECS HAVE BEEN UPDATED

Resolution Specification for the ENC4118_0

To convert from encoder pulses to length, use the resolution specification that is provided on the product page of your draw-wire sensor.

This value can be found on the Specifications tab and is presented as micrometers per pulse. For more information, review the example code below.

Example Code

The code below is derived from the Phidget Code Sample Generator. It shows how to convert position data from an encoder interface into a length measurement.

Click on your preferred programming language to view the code example.

from Phidget22.Phidget import *
from Phidget22.Devices.Encoder import *
import time

def onPositionChange(self, positionChange, timeChange, indexTriggered):
	resolution = 10E-6 #The ENC4118_0 has a resolution of 10um/pulse, replace with your product's resolution
	meters = self.getPosition() * resolution
	print("Length: " + str(round(meters, 3)) + " m")

def main():
	encoder0 = Encoder()

	encoder0.setOnPositionChangeHandler(onPositionChange)

	encoder0.openWaitForAttachment(5000)

	time.sleep(5)

	encoder0.close()

main()

import com.phidget22.*;
import java.lang.InterruptedException;

public class Java_Example {

    public static void main(String[] args) throws Exception {
        Encoder encoder0 = new Encoder();

        encoder0.addPositionChangeListener(new EncoderPositionChangeListener() {
            public void onPositionChange(EncoderPositionChangeEvent e) {
                try {
                    Encoder evChannel = (Encoder) e.getSource();
                    double resolution = 10E-6; //The ENC4118_0 has a resolution of 10um/pulse, replace with your product's resolution
                    double meters = evChannel.getPosition() * resolution;
                    System.out.println("Length: " + Math.round(meters * 1000.0) / 1000.0 + " m");
                } catch (PhidgetException ex) {
                    ex.printStackTrace();
                    System.out.println("PhidgetException " + ex.getErrorCode() + " (" + ex.getDescription() + "): " + ex.getDetail());
                }
            }
        });

        encoder0.open(5000);

        Thread.sleep(5000);

        encoder0.close();
    }
}

using System;
using Phidget22;

namespace ConsoleApplication
{
	class Program
	{

		private static void Encoder0_PositionChange(object sender, Phidget22.Events.EncoderPositionChangeEventArgs e)
		{
			Phidget22.Encoder evChannel = (Phidget22.Encoder)sender;
			double resolution = 10E-6; //The ENC4118_0 has a resolution of 10um/pulse, replace with your product's resolution
			double meters = evChannel.Position * resolution;
			Console.WriteLine("Length: " + Math.Round(meters, 3) + " m ");
		}

		static void Main(string[] args)
		{
			Encoder encoder0 = new Encoder();

			encoder0.PositionChange += Encoder0_PositionChange;

			encoder0.Open(5000);

			System.Threading.Thread.Sleep(10000);

			encoder0.Close();
		}
	}
}

#include <phidget22.h>
#include <stdio.h>
/* Determine if we are on Windows of Unix */
#ifdef WIN32
#include <windows.h>
#else
#include <unistd.h>
#define Sleep(x) usleep((x) * 1000)
#endif

static void CCONV onPositionChange(PhidgetEncoderHandle ch, void * ctx, int positionChange, double timeChange, int indexTriggered) {
	int64_t position;
	double resolution = 10E-6; //The ENC4118_0 has a resolution of 10um/pulse, replace with your product's resolution
	PhidgetEncoder_getPosition(ch, &position);
	double meters = resolution * position;
	printf("Length: %.3f\n m", meters);
	printf("----------\n");
}

int main() {
	PhidgetEncoderHandle encoder0;

	PhidgetEncoder_create(&encoder0);

	PhidgetEncoder_setOnPositionChangeHandler(encoder0, onPositionChange, NULL);

	Phidget_openWaitForAttachment((PhidgetHandle)encoder0, 5000);

	Sleep(5000);

	Phidget_close((PhidgetHandle)encoder0);

	PhidgetEncoder_delete(&encoder0);
}

Speed Calculations

If you are interested in calculating the speed of your draw-wire sensor, a simple Python example is provided below.

In order to implement more accurate speed calculations, review the Encoder Velocity: A Common Miscalculation guide for more information.

from Phidget22.Phidget import *
from Phidget22.Devices.Encoder import *
import time

def onPositionChange(self, positionChange, timeChange, indexTriggered):
    resolution = 10E-6 #The ENC4118_0 has a resolution of 10um/pulse, replace with your product's resolution
    speed = (positionChange * resolution) / (timeChange/1000.0)
    print("Speed: " + str(round(speed, 3)) + " m/s")

def main():
    encoder0 = Encoder()

    encoder0.setOnPositionChangeHandler(onPositionChange)

    encoder0.openWaitForAttachment(5000)

    time.sleep(5000)

    encoder0.close()

main()

Installation and Mounting

M5 mounting holes are available on the back of the housing and on the end of the draw wire. For more information, view the mechanical drawings for your product which can be found on the product page under the Specifications tab.

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Related Links/Guides

• Linear Potentiometers
• Linear Encoders