Data, Algorithms, Bounds

Objective

The objective is to explore the use of data and the development of temperature conversion and linear interpolation algorithms for calculating psi from a given temperature.

Introduction

Your LabVIEW VI will calculate the resultant saturated pressure of our mythical vessel of special fluid and air to a numeric indicator vesselPressPsi, from a temperature (degrees Fahrenheit: vesselTempFahr). This temperature represents an electrical sensor input that was converted to engineering units. The linear interpolation algorithm is based on degrees Celsius.

Requirements

Design, Code, and Test a LabVIEW VI which will loop forever calculating the resultant saturated pressure of our mythical vessel of special fluid and air to the proper numeric indicator; vesselPressPsi, from a temperature (degrees Fahrenheit, numeric indicator vesselTempFahr). Temperature will be provided by using a random number generator representing an input OR the opportunity as data from a user by implementing a control switch to allow the user to input temperature. Use the modulus operator to place your random number closer to the range vesselTempFahr (122-176F), do not use the modulus operator on the operators input. This temperature represents an electrical sensor input that was converted to engineering units. The linear interpolation algorithm and corresponding data tables are based on degrees Celsius (numeric indicator vesselTempCelsius). The VI will have two pairs of data points as default values or operator controlled; See Appendix A, which provide corresponding pressure for a given Celsius temperature. One data pair is the upper and lower degree Celsius and the other pair is the upper and lower relative saturated pressure for the corresponding temperature. These data pairs will be numeric controls, allowing the user to change the bounds. Compute the saturated pressure from the temperature input. Control the output rate to 0.5 seconds when the VI is in the random number mode, 1.5 seconds when in user mode.

Since temperature in this assignment represents an electrical sensor input, we need to understand some basic constraints with sensors. Sometimes sensors are saturated or at their limits of operations, the sensor may respond (signal) with unknown values outside its working range. This could cause erratic or catastrophic conditions for control systems. This is solved by placing limiter testing at saturation points of sensors. Saturation testing imposes upper and lower bounds on a signal. When the input signal is within the range specified by lower limit and upper limit parameters, the input signal passes through unchanged. When the input signal is outside these bounds, the signal is clipped to the upper or lower bound values. If the result is outside the bounds turn on one of the two limit breach indicators: one representing the upper bound limit breach the other the lower bound breach.

Algorithm

Not every Temperature input will have a direct corresponding pressure. For example if vesselTempCelsius = 65, which is neither of the known Celsius limits in Appendix A. Linear interpolation is a way to fill in the holes'' in tables. Linear Interpolation is a method of constructing new data points within the range of a discrete set of known data points. Linear interpolation is quick and easy, but at times not very precise, to increase precision is to increase the number of data points with in the know set of data points.

In this assignment, you only have two data points, which represent the upper and lower data range.

Interpolation example with Appendix A:

vesselTempFahr = 147.0

Result of hand test is psi= 0.2978 psi

Design considerations:

1. I suggest developing the loop around your algorithm first, provide a termination of the execution.

a. Add a control switch and case block, check mechanism behavior and labeling

2. Be careful on your data-flow as to what gets done in sequence

3. I suggest a button or switch to control random number or user input.

4. Use a timing mechanism from the programming/timing pallet, to slow down your HMI display update when appropriate usage state.

5. Indicator LEDs are a good source for Alerts/Alarms

6. Make sure you allow the bounds data in the appendix to be controlled by the operator.

7. 5 extra points to your VI run when opened.

Deliverables 40pts: due end of class or following Wednesday by noon.

1. LabVIEW VI named Hw2.

2. The LabVIEW VI will be documented in the Icon containing no less than the following:

a. Student name

b. Student id

c. Assignment Name

d. Description of assignment

e. How to use your VI, description

f. Input type / limits of VI, if any

g. Output type / limits of VI, if any

Appendix A

Temperature

- t -

(oc)

Pressure

- pv -

(psia, lb/in2)

60

0.2563

70

0.3631