Software

LabVIEW (Laboratory Virtual Instrument Engineering Workbench) was chosen as the software for this project. It was selected because of its ability to easily create professional user Interfaces and

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also it could be used to automate any instrument using free instrument drivers (National Instruments, 2013). LabVIEW is a system-design platform and development environment for a visual programing language from National Instruments. It is commonly used for data acquisition, instrument control and industrial automation on a variety of platforms which include Microsoft windows (“LabVIEW,” 2016).

Programs in LabVIEW are called virtual Instruments (VIs) because their operations and appearance imitate physical instruments. A VI contains three components: Front panel which is a user interface for the VI, it contains controls(input) and indicators(output); Block diagram (shown in Appendix 11 figure 8.17) which is the source code for the functionality of the program, block diagram objects include terminals, SubVIs, Express VI, functions (SubVIs, Express Vis and functions are explained in the paragraph below), constants, structures and wires that transfer data among other block diagram objects; Icon and connector pain, which identifies the interface to the VI so that the VI can itself be used in another VI (National Instruments, n.d.).

SubVIs- corresponds to a subroutine in text-based programming languages. Once you build a VI it can be used in another VI. The VI can be called in the block diagram of another VI and then its known as a SubVI (National Instruments, n.d.). Express VIs-are nodes that require minimal wiring because you configure them with dialog boxes. Express VIs give users a VI or a library of VIs for making their own applications and it is commonly used to perform measurement tasks (National Instruments, n.d.). Functions- are elementary nodes in the G programming language. They are analogous to operators or library functions in conventional languages (National Instruments, 1998).

3.6.2.1 Key steps to consider when making the program

The key steps required to capture the temperature off the thermistor and present it to the user, were identify and how the LabVIEW software was used to program them are listed below

3.6.2.1.1 Provide Voltage in (Vin) to the Potential divider circuit

The first step was to provide an input voltage (Vin) to power the potential divider circuit. This was done using a DAQ Assistant Express Vi in LabVIEW. This Express Vi can be used to create, edit and run tasks using the NI-DAQ USB 6008. Therefore this was used to generate an analogue voltage signal (Vin) from the Analogue output (AO0) of the USB 6008 unit.

3.6.2.1.2 Obtain Voltage (Vout) of the potential divider circuit

To acquire the voltage signal (Vout) from the voltage divider circuit, the DAQ Assistant Express Vi was set up to acquire analogue voltage signal from the analogue input (AI0) of the NI DAQ USB- 6008.

86 3.6.2.1.3 Calculating the Temperature

Since the values of Vin, Vout and the resistance (R1) are known the thermistor resistance (Rt) can be calculated using the equation 3.7. The formula Express VI in LabVIEW was used to apply equations in the block diagram. Thereafter the temperature was calculated using equation 3.1 given above. This equation provides the temperature in Kelvin so to obtain the temperature in degrees Centigrade 273.15 had to be deducted from the temperature reading obtained.

3.6.2.1.4 Graphical User Interphase

The graphical user interphase has to be user friendly and provide all the information to the user. The user should be able to set the input Voltage (Vin) and the resistance (R1) of the potential divider circuit. Therefore two controls were placed on the front panel of the screen for this purpose. It is important to display the temperature captured from the ETS yarn in a graphical manner therefore the temperature reading was shown using a thermometer. It was also important to see how the temperature reading varies with time. Therefore a waveform graph was used to show this. Since this software will be used when running experiments on the ETS yarn it was considered essential that the user gets to see the voltage out (Vout) and the thermistor resistance (Rt). Therefore two indicators were placed in the front panel to give the Rt and Vout values. The graphical user interface is given below in figure 3.17.

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Figure 3-17: User interface for temperature measurement from the ETS yarn

3.6.2.1.5 Store data

It is important to store the temperature recorded by the thermistor yarn in order to analyse the data later on. Therefore by using the Open/Create/Replace File Function in LabVIEW an excel (.xlxs) file was created. The file dialog Express VI was used to give the user the opportunity to select a location and a name for the new file. Thereafter by using write to text file function the temperature reading, temperature range, if the temperature range has been breached, voltage out (Vout) and the thermistor resistance (Rt) were recorded on the excel file (showed in table 3.3).

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Table 3:3: Excel sheet that records data from the application

3.6.2.1.6 Additional feature

When used in experiments or in other applications (such as detecting inflammation in wounds), it would be important to see if the temperature measured goes above or below a temperature range pre-set by the user. Therefore the software also enables one to define temperature limits (Tmax. & Tmin.). If the temperature reading (T) goes above or below the temperature limit a warning signal would appear and an indicator would light up informing the user that the measured temperature (T) does not lie within the set range. The figure 3.18 below shows an image of the user interface once the temperature has breached the temperature limits set by the user.

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Figure 3-18: User interface with the temperature rising above the maximum limit set (The green indicator on the bottom left is lit up and there is a warning message displaying the “temperature (T) is above the temperature range” right below the graph)

3.6.2.2 Flow Chart of the Program

A detailed flowchart of how the software runs is given below. The main VI was created by calling three SubVI’s. A VoltageIN SubVI was used to generate a Vin to the potential divider circuit. Capture temperature SubVI was used to capture the Voltage out (Vout) from the potential divider circuit and convert it to temperature. The check range SubVi was used to check if the temperature measured fell within or out of the temperature range set by the user.

90 3.6.2.2.1 Flowchart of the Main VI

91 3.6.2.2.2 Flowchart of Voltage In SubVI

92 3.6.2.2.4 Flowchart of Check Range SubVI

3.7 Summary

This chapter looked at the construction of the ETS yarn. The initial test done on the chosen thermistor proved that it could be used for surface temperature measurement. Thereafter the geometrical model of the ETS yarn constructed in MATLAB and it was first used to estimate the minimum volume of solder paste required for forming the interconnects as 2.44 ∗ 10−12 𝑚3. Then the micro-pod was modelled in a cylindrical shape and the minimum volume of polymer resin required for this encapsulation was estimated as 1.46 ∗ 10−10 𝑚3. The model also looked at the layers covering the micro-pod (knit braided sheath and the packing fibre layer). It also provided an equation to calculate the volume fraction of the packing fibres. This model was also used to estimate the parameters in the COMSOL model in Chapter 4 section 4.2.2.

During the construction of the ETS yarn it was proven that it was impossible to create an encapsulation with a 0.732 mm diameter and a more realistic diameter would be 0.87 mm. It also showed that the volume of solder paste required for the solder joint would be five times greater than the estimated value. It was decided that a simple voltage divider circuit would be used as the hardware for the ETS yarn. LabVIEW was chosen as the programing language to capture and present

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the temperature off an ETS yarn. A complete breakdown of the LabVIEW program was also presented in this chapter.

The next stage was to test the ETS yarn, to see how the micro-pod and the yarn filaments effect the thermistor’s measurements, this is described in chapter 4.

3.8 References

 AMETHERM, 2013. NTC Thermistors - Temperature Measurement With A Wheatstone Bridge | Ametherm [WWW Document]. URL http://www.ametherm.com/thermistor/ntc- thermistors-temperature-measurement-with-wheatstone-bridge (accessed 2.11.16).  Anonymous, 1995. Thermocouples, RTDs, and thermistors. Mach. Des. 67, 74.

 Armstrong, D.G., Holtz-Neiderer, K., Wendel, C., Mohler, M.J., Kimbriel, H.R., Lavery, L.A., 2007. Skin Temperature Monitoring Reduces the Risk for Diabetic Foot Ulceration in High- risk Patients. Am. J. Med. 120, 1042–1046. doi: 10.1016/j.amjmed.2007.06.028.

 BIPM, (Bureau International des Poids et Mesures), 2014. Guide on secondary thermometry Thermistor Thermometry. Consultative Committee for Thermometry under the auspices of

the International Committee for Weights and Measures. URL

https://www.bipm.org/utils/common/pdf/ITS-90/Guide-SecTh-Thermistor- Thermometry.pdf. (accessed 2.11.15).

 Cork, C., Dias, T., Acti, T., Ratnayake, A., Mbise, E., Anastasopoulos, I., Piper, A., 2013. The next generation of electronic textiles. Presented at the Digital Technologies for the Textile Industries, Manchester, UK.

 Dias, T.K., RATHNAYAKE, A., 2016. Electronically functional yarns. WO2016038342 A1.  Dini, V., Salvo, P., Janowska, A., Di Francesco, F., Barbini, A., Romanelli, M., 2015.

Correlation Between Wound Temperature Obtained With an Infrared Camera and Clinical Wound Bed Score in Venous Leg Ulcers. Wounds Compend. Clin. Res. Pract. 27, 274–278. PMID: 26479211.

 Janesch, J., 2013. Two-Wire vs. Four-Wire Resistance Measurements: Which Configuration Makes Sense for Your Application? Keithley Instruments. Inc.

 Kiethley, 2012. Overview of Two-Wire and Four-Wire (Kelvin) Resistance Measurements (No. 3176). Keithley Instruments. Inc, USA.

 Kimball, B.R., Decristofano, B., Caldarella, G., 1993. Thermistor calibration procedure for simulated skin sensors (No. NATICK/TR-93/024). U.S. Army Natick Research, development and engineering center.

 LabVIEW, 2016. . Wikipedia Free Encycl. URL https://en.wikipedia.org/wiki/LabVIEW (accessed 2.3.14).

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 Liu, Y., Wang, L., Liu, J., Di, Y., 2013. A study of human skin and surface temperatures in stable and unstable thermal environments. J. Therm. Biol. 38, 440–448. doi: 10.1016/j.jtherbio.2013.06.006.

 MathWorks, 2018. MATLAB Documentation - MathWorks United Kingdom [WWW Document]. URL https://uk.mathworks.com/help/matlab/?requestedDomain=true (accessed 2.5.18).

 McGuiness, W., Vella, E., Harrison, D., 2004. Influence of dressing changes on wound temperature. J. Wound Care 13, 383–385. doi: 10.12968/jowc.2004.13.9.26702.

 M. Romanelli, G. Gaggio, M. Coluccia, F. Rizzello, A. Piaggesi, 2002. Technological Advances in Wound Bed Measurements. Wounds 14.

 National Instruments, 2013. Top 10 Reasons to Use NI LabVIEW for Automating Test and Validation Systems - National Instruments [WWW Document]. URL http://www.ni.com/white-paper/8995/en/ (accessed 6.21.16).

 National Instruments, 1998. Function and VI Reference Manual.

 National Instruments, n.d. LabVIEW Environment Basics - National Instruments [WWW Document]. URL http://www.ni.com/getting-started/labview-basics/environment (accessed 6.21.16).

 Nawrocki, W., 2005. Measurement Systems and Sensors. Artech House, Norwood, MA, USA.  Rathnayake, A., 2015. Development of the core technology for the creation of electronically

active, smart yarn (PhD thesis). Nottingham Trent University.

 Recktenwald, G., 2013. Voltage Dividers and Potentiometers. URL https://cdn.sparkfun.com/assets/resources/4/4/pot_voltage_divider.pdf (accessed 6.3.14).

 Schweber, B., 2016. The Wheatstone Bridge: Still the Preferred Sensor-Interface Topology After 180 Years | Electronics360 [WWW Document]. Electron. 360. URL http://electronics360.globalspec.com/article/6522/the-wheatstone-bridge-still-the- preferred-sensor-interface-topology-after-180-years (accessed 1.22.18).

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4. Performance Analysis of the Yarn