Vernier Photogate Timing Lab

This lab introduces the student to the Vernier Photogate Sensor and teaches concepts in

velocity. The student must learn how to connect to the ELVIS II prototyping board to

make the necessary signal connections for the sensor.

Theory:

Vernier offers a sensor that measures the movement of objects passing through or outside

of the gate arms. In the internal gate mode, an infrared beam is detected by a fast IR

detector. Any object passing through the gate interrupts the signal.

How to build the experiment:

The Photogate Sensor is attached to the Digital Proto Board Connector (BTD-ELV),

which is connected to the NI-ELVIS II prototyping board.

Figure 1 and the following steps show how to wire the connector.

Figure 1: Prototyping Board for the Vernier Photogate Sensor Timing Lab

Wire the following pins:

1) CTR0 - Gate pin from the Elvis Counters to DIO0 pin of the Digital Proto Board

Connector

2) ELVIS DC Power Supply +5V to 5 V pin of the Digital Proto Board Connector

3) ELVIS DC Power Supply Ground to GND pin of the Digital Proto Board

Connector

How the Photogate Timing VI runs:

1) DAQmx VIs: A counter input pulse width task is created to read the signal from

counter 0 on the NI ELVIS II.

2) Calculating Velocity: The time the IR beam was blocked, which is the pulse

width, corresponds to the time it took for the object to pass through the gate arms.

Dividing this time by the length of the object gives you the velocity.

3) Displaying the Data: The time it took for the object to pass through the gate is

displayed under “blocked duration (seconds).” The calculated velocity of the

object is shown in m/s.

Figure 2 below shows the LabVIEW code.

Figure 2: Photogate Timing VI Block Diagram

Running the Photogate Timing VI:

Before running the Photogate Timing VI, verify that the counter selected is ctr0 on your

ELVIS II device. Enter the length of the object passing through in meters. Check that

the shutter on the Photogate Sensor arm is open. You will be using the internal gate

mode, so the red LED on the sensor should not be lit.

Press the Run button and pass an object through the Photogate Sensor arms. The

program will run once and display the object’s velocity.

Figure 3: Photogate Timing VI Front Panel

Summary:

With the Vernier sensors, you can take advantage of NI ELVIS II to acquire data by

plugging in with a simple Proto Board Connector. Use the Photogate Sensor and

LabVIEW to determine the velocity of an object passing through the sensor arms.