Product specifications

Instrumentation Laboratory Exercise 36

To do this, create the following formula boxes. The V

array is wired

into the left side, and the output at the right side is the array

converted to volts. The first formula box extracts the MSB and

removes the twos complement (by adding 128 to the value of the

array). The second formula box extracts the LSB. Notice we are using

a predefined function in the box called intpar. It returns the integer

part of a whole number. This is used to eliminate the fractional

component. The third formula box on the right reconstructs the

number in the proper form MSB × 256 + LSB, because each digit of

the MSB is equal to 256 of the LSB.

Also we divide by the factor of 217/V

range

where V

range

is the

maximum input voltage minus the minimum input voltage and 217 is

the number of voltage levels we can differentiate (for example, 0 to

216 + 215 + 214 + … + 2). As we have used a unipolar input with a

range of 10 V, therefore the maximum is 10 V and the minimum is 0

V, so V

range

is simply 10 V (if we had used bipolar V

range

would be

–10 V to +10 V, or 20 V), thus our conversion factor is 13107.2. This

is what the byte swapping routine and conversion should look like:

Finally, display the resulting data as a Strip Chart (under the Display

Menu) as shown below. Right click Strip Chart and select Properties

from the context menu. Go to the X-Y Scales properties on the left

side bar and set X minimum to 0 and maximum to 2000. Set Y scale

appropriately to see the trace. Ensure Autoscaling is OFF for both

scales.