ME 322: Instrumentation Lecture 18 March 2, 2015 Professor Miles Greiner TC signal conditioner, Computer data acquisition introduction, Lab 7, myDAQ, LabVIEW program

Announcements/Reminders HW 7 due Friday Lab 6 (wind tunnel) this week – See WebCampus for schedule – Please be on time. – Bring Excel from HW 6 and use it to process the data you acquire. – This will help check the data as you take it and allow you to complete the data acquisition phase of the lab in one hour

Thermocouples Consist of two dissimilar metal wires, A(+) & B(-) connected to a digital voltmeter (copper terminals C) Output voltage V OUT depends on the sensing junction temperature T S – However, V OUT ’s sensitivity S = 20–50  V/ ° C is very small – Moreover, V OUT also depends on (undesired inputs) Terminal temperature T T High Frequency Radio Frequency Noise Ground loop currents T TSTS V OUT + -

Type J (Iron/Constantan) thermocouples – + Iron (white insulation) – - Constantan (red or white with red stripe insulation) Omega DRE–TC-J TC Signal Conditioner ; webweb – rumentation/Labs/Lab%2007%20Boiling%20Water%20Temperatu re/Lab7%20Index.htm rumentation/Labs/Lab%2007%20Boiling%20Water%20Temperatu re/Lab7%20Index.htm – Wiring: Iron (white insulation) goes to +Tc; Constantan (red stripe) goes to (-Tc) Output Voltage, V SC : Com = -; V OUT = + Power: 110 VAC (top) In ME 322 Labs Constantan ( ) + -

Transfer Function (Type-J-TC/DRE–TC-J TC) Reading V SC [V] Measurand, T [°C] ? Out of range Transfer Function

Computer Data Acquisition (DAQ) Sensors detect measurands and produce signals – Voltages, currents, resistances, pulses,… Conditioners convert those output signals to easily measureable voltages A multiplexer (MUX) sweeps channel to channel and feeds individual signals, at different times, to the Analog-to-Digital (A/D) converter The A/D converter rapidly samples real signals ( …V) and converts them to integers (0, 1, 2,…) that the digital computer can work with. Computer programs store and/or process the data – In ME 322 we use LabVIEW and DAQmx drivers (in ECC)

Lab 7 Boiling Water Temperature in Reno Elevation 4500 ft, P ATM = 86 kPa (101.3 kPa at sea level) Beaker, water, immersion heater Type-J TC, DRE–TC-J TC Signal Conditioner National Instruments myDAQ (USB to computer)

National Instruments myDAQ $179 on Studica – 01_2.html?utm_source=google&utm_medium=ppc&kpid=734446&gclid=CJXw956H8LwCF Ylafgodb3wAMg 01_2.html?utm_source=google&utm_medium=ppc&kpid=734446&gclid=CJXw956H8LwCF Ylafgodb3wAMg Reads TC Signal Conditioner output (or other device) – Connect to Analog Input (AI) Channel 0 (could use channel 1) COM to 0- and AGND (negative analog input and ground) Vout to 0+ (positive analog input) This is a Differential Input – Difference between two channels, gives better common-mode rejection

Check Connections Open NI–MySystem-Measurement & Automation Explorer – This program comes with LabView MySystem (upper left corner) – Device & Interfaces (Double Click) MyDAQ (Right Click) – Device Pin outs – Test Panel

Lab 7 LabVIEW Data Acquisition Program Called a VI – Virtual Instrument – Front Panel – Indications and Controls – Block Diagram – Devices, connections and logic Lab 7 Objectives – Measure V OUT from AI channel 0 for 3 seconds Sample rate 1000 times per second Convert to T S = (40 ° C/V)V OUT – Plot Temperature versus time on front panel Write data to an Exel file – Find average temperature, T AVG

LabVIEW Five Main Acquisition Steps Measurement I/O, NI DAQmx 1)Create a channel 2)Timing 3)Start Process 4)Read Data analog waveform – 1 Channel – N-Samples – Output voltage – convert to ̊ C 5)Clear the test Programming; Dialog and User Interface simple error handler You will need to download and install DAQmx to on your computer (after installing LabVIEW) find these icons. In this class we give and modify example LabVIEW programs to help you quickly learn to perform data acquisition. However, we don’t deal with structured programming.

LabVIEW program (block diagram)

LabVIEW Front Panel

MUX

Lab 7 VI Objectives Measure atmospheric pressure P ATM – Find T SAT at that pressure Allow water in beaker to reach a full, rolling boil Measure V OUT for 3 sec – Sample 1000 times per second – Convert to T S = (40 ° C/V)V OUT Plot Temperature versus time – Write to a file Find average temperature, T AVG Repeat for ice/water mixture and room temperature water Compare to liquid in glass thermometer Is T AVG,Boil ± w Tavg ~ T SAT Determine effect of salt in the water