The WKU Multi-Purpose Laboratory Interface

We have developed a laboratory interface box (depicted above) that will be used as a bridge between various sensors (such as sonic ranger position sensors, force probes, thermocouples, strain gauges, etc) and the computer.  This unit will provides a convenient means for connecting sensors to the computer, and provides signal conditioning (amplification, excitation, linearization, etc) to analog input signals.  This unit is connected by a 50 pin ribbon cable to a National Instruments Lab-PC-1200 data acquisition card that in inside the computer.  The interface has connections for

• 8 Digital I/O Lines

• 2 Analog Output Channels

• 6 Analog Input Channels 

• 2 Ultrasonic Ranger Position Sensors

• 2 Counter/Timers

• DC Level Voltages (+5V, +12V, -12V, GND)

• an 120V AC Relay Controlled by a Digital Line

• a DPDT Relay Controlled by a Digital Line

Digital Input/Output

A digital channel can take on either one of two possible states associated with a voltage level near ground or near +5V.  These two states are commonly labeled as ON/OFF, HI/LOW, TRUE/FALSE, OPEN/CLOSED etc. depending upon the application.  A specific digital port is specified by giving the digital channel (A or B) and the digital line (0, 1, 2 or 3).  The digital I/O ports on the WKU Multi-Purpose Laboratory Interface accept a stereo-type phono plug which is depicted below.  

A common use of digital I/O in the University Physics Laboratory is to measure the output state of a photogate sensor.  The photogate sensor consists of a light emitting diode on one edge of the U-shaped device and a detector on the other side.  If the beam of light is blocked by an object then the output of the photogate is FALSE.  If the beam is unblocked then the output is TRUE.

Analog Input/Output

An analog channel can take on a finite number of values between a specified maximum and minimum.  The analog channels on the WKU system can take on any of 2¹² different values between -5V and +5V.  There are two analog output channels (AO-0 and AO-1) which are used to set a particular signal level.  There are six analog input channels (AI-2 thru AI-7) which are used to measure the level of a signal.  The connections for the analog channels have been customized to the DIN connectors that are common on sensors made by Pasco and Vernier Scientific.  

Signal Conditioning

Directly above each analog channel is a socket that will accept a 5B series signal conditioning module.  Different signal conditioning modules are appropriate for different sensors.  For example, the 5B31-07 module is used to measure signals that can vary from -20 V to + 20 V, while the 5B30-02 module is used to measure signals that can vary from only -50 mV to + 50 mV.  There are also specialty modules for some sensors such as thermocouples and strain gauges.  The table below summarizes the type of sensors that are available and their common uses.

Sonic Ranger

The connections that are used for sonic rangers on the WKU Multi-Purpose Laboratory Interface are depicted in the figure below.  First there is a CLOCK input.  A square-wave signal that triggers the Sonic Ranger to send a pulse is applied here by connecting to analog output channel 0.  There are SEND and RECEIVE connections for each Sonic Ranger.  These are stereo phono sockets and are color coded to match the plugs on the end of the Sonic Ranger.  Each ranger also has an output signal labeled OUT.  The number of pulses on the output channel can be counted with a timer (B1 for ranger 1 or B2 for ranger 2) to determine the amount of time required for the pulse emitted by the ranger to go out, be reflected and return to the detector.  This time is of course then converted to a distance by applying the appropriate calibration.  The required connections for using either one or two sonic ranger position sensors are described and depicted below.

Required Connections for One Sonic Ranger

Analog Output Zero (AO 0) to Sonic Ranger Clock Sonic Ranger Yellow Plug to SEND 1. Sonic Ranger Black Plug to RECEIVE 1. Output of Sonic Ranger 1 to GATE of Timer B1. Output of Timer B0 to CLOCK of Timer B1.

Required Connections for Two Sonic Rangers

Analog Output Zero (AO 0) to Sonic Ranger Clock Sonic Ranger 1 Yellow Plug to SEND 1. Sonic Ranger 1 Black Plug to RECEIVE 1. Sonic Ranger 2 Yellow Plug to SEND 2. Sonic Ranger 2 Black Plug to RECEIVE 2. Output of Sonic Ranger 1 to GATE of Timer B1. Output of Sonic Ranger 2 to GATE of Timer B2. Output of Timer B0 to CLOCK of Timers B1 & B2.