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TRANSCRIPT
NOxTrac™ Evaluation Kit Draft Documentation
7/21/17
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Table of Contents
Introduction ........................................................................................................................... 3
Kit Contents ............................................................................................................................ 3
Installation ............................................................................................................................. 4 Step 1. Download and Install the Demonstration Software and Drivers ........................................... 4 Step 2. Install the Sensor(s) in a Test Pipe ........................................................................................ 4 Step 3. Connect the Sensor to the Electronics .................................................................................. 4 Step 4. Connect the Electronics to a Power Source and the CAN Adapter ......................................... 6 Step 5. Connect the CAN adapter to the Host Computer .................................................................. 7
Basic Operation ...................................................................................................................... 8 Step 1. Apply Power to the Electronics Module(s) ............................................................................ 8 Step 2. Start the Platform Evaluation Tool ....................................................................................... 8 Step 3. Connect the CAN Interface using the “Connect” Button ........................................................ 8 Step 4. Confirm that the Electronic Module(s) are located ............................................................... 9 Step 5. Enable One or More Sensors .............................................................................................. 10 Step 6. Log Data ............................................................................................................................. 11 Step 7. Capture Raw Waveforms (Optional) ................................................................................... 12
Sensor Details ....................................................................................................................... 13
Interpreting Measurements .................................................................................................. 16 Measurement Basics ...................................................................................................................... 16 Transfer Function Basics ................................................................................................................ 18 All Logged Measurements .............................................................................................................. 20 Noise and Filtering ......................................................................................................................... 20
Appendix A – Notes Regarding Sensor Drift .......................................................................... 24
Appendix B – CAN Protocol ................................................................................................... 25
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Introduction Thank you for your interest in NOxTrac™ technology. If you have any questions or problems with your kit please contact Dr. Leta Woo ([email protected]) or Joe Fitzpatrick ([email protected]) directly for assistance.
Kit Contents
Your kit should contain the following:
-‐ 2 Sensor Probes with cables -‐ 2 Control/Electronics modules (programmed to match the probes) -‐ 1 USB to CAN adapter -‐ 1 DB9 CAN Cable
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Installation Step 1. Download and Install the Demonstration Software and Drivers The latest version of all software, documentation, and drivers can be found here: http://emisense.com/noxtrac-‐downloads/ At this time only Microsoft Windows is supported for software. We recommend the following download/installation order:
1. Download the latest manual (this document) and check for changes 2. Download and install the NI-‐CAN drivers for the National Instrument USB to CAN
adapter 3. Download and install the NOxTrac™ Platform Evaluation Tool
Step 2. Install the Sensor(s) in a Test Pipe The sensors are a M18 thread and should fit in a standard oxygen sensor bung. If you are operating in a vehicle or engine dyno we recommend installation between “10 o’clock” and “2 o’clock” in the pipe. In other words, the probe should be installed on the top of the pipe to avoid shock cooling the sensor element with condensation. Step 3. Connect the Sensor to the Electronics IMPORTANT: Sensors should always be paired with the electronics module specifically marked for them! The module is flashed with information that is used to heat the sensor to operating temperature. Swapping modules without reprogramming this information will lead to erratic results and potentially damage the sensor. The sensor has four leads:
1. Working Electrode (WE) 2. Counter Electrode (CE) 3. Heater + 4. Heater –
These are fanned out to two BNC and two Banana connectors which plug into the output end of the electronics.
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IMPORTANT: The cable adapter connects to the sensor via an automotive style sensor. If you disconnect and reconnect this connector be sure to carefully examine the back of the pins on both sides. They are easily dislodged. If you see the pin or grommet no longer recessed from the back of the connector you will need to push it back in with a small screwdriver or pliers.
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Step 4. Connect the Electronics to a Power Source and the CAN Adapter
The Control end of the electronics require three connections:
1. Power + (12 to 13.8VDC at 2.5A max) 2. Power – (Ground) 3. CAN
Power can be either vehicle power or a bench power supply. The sensors draw approximately 1 to 1.2 amps continuously when operating, but can draw short bursts of 2.5 amps when the element is first heated. If you only operate one module you can connect the provided DB-‐9 cable directly from the electronics module to the USB to CAN interface. If you wish to operate multiple modules concurrently you will need to provide suitable CAN bus wiring. The DB-‐9 connector on the electronics module conforms to the CiA DS-‐102 standard:
Pin 2 = CAN L Pin 3 = CAN Ground Pin 7 = CAN H
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The provided CAN Interface also conforms to this standard. We ship all modules with CAN termination “ON”. Depending on your wiring and setup you may need to disable CAN termination on one or more modules. If you have a revision G module or later, termination is controlled with a small switch to the right of the CAN DB-‐9 connector (see photo above). On earlier revisions the switch is internal and just behind the DB-‐9 connector on the PCB: Step 5. Connect the CAN adapter to the Host Computer If the NI-‐CAN drivers were properly installed in Step 1 above the “USB” indicator on the interface should turn steady yellow after the driver initializes:
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Basic Operation Step 1. Apply Power to the Electronics Module(s) All status LEDs on the module(s) should briefly flash, then the yellow LED should begin blinking. NOTE: If an error condition occurs, the red LED will be lit continuously. Step 2. Start the Platform Evaluation Tool A screen like the following should appear:
Step 3. Connect the CAN Interface using the “Connect” Button
NOTE: By default “CAN1” is selected. If you are operating other National Instrument NI-‐CAN devices on the same computer you may need to change this.
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Step 4. Confirm that the Electronic Module(s) are located If the modules have power and CAN is wired and terminated correctly, any connected modules should appear in the module status area in the upper left hand corner of the screen in 1 or 2 seconds:
The live data area for each detected module will also become active:
But the values have no meaning until the sensor is operating.
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Step 5. Enable One or More Sensors A sensor is turned on (heated) by clicking on the Enable checkbox in the status area:
The Sensor Status should change to “HEATING” and the two small power gauges in the sensor live data area should become active:
NOTE: These ‘proof of concept’ elements have ceramic imperfections as fabricated (see the Sensor section for more information) so the heating and cooling cycles are very cautious. The module will start at 10% PWM duty cycle on the heater, then slowly ramps measured heater power up to 8 Watts. 8 Watts will be held for an additional 90 seconds to thermally soak the sensor. Only then will the module switch to closed loop heater control using measured cell impedance. Once the cell is properly heated and the system changes to “OPERATING” status, the data in the
charts will become valid:
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If the module contains calibration information for O2, NO, and H20 the two rotary gauges for NOx and O2 will become live as well. If the module does not contain a calibration, see the Interpreting Measurements section for transfer function basics. Step 6. Log Data Logging is controlled using the lower left portion of the screen:
The top field is the folder where log files will be stored. By default it is the Windows User Directory for the currently logged in user. The second field is the ‘base name’ for log files. Each time logging is started and stopped a new file is created. The name of that file will be the ‘base name’ (NOxTracPET by default) with the current date and time appended (ex. NOxTracPET-‐20170721-‐120946). To start logging, click the ‘Logging’ toggle with the mouse. The edit fields will become disabled and an elapsed time counter will appear:
To stop logging, click on the toggle again to uncheck it. The stored log files are a comma delimited text file which can be read by Excel, Matlab, and most other spreadsheet and data analysis tools. The logs contain considerably more information than is displayed on the screen. See the Interpreting Measurements section for more information.
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Step 7. Capture Raw Waveforms (Optional) If the sensor is “OPERATING” and no log is currently being recorded a “Capture Waveform…” Button is available in the sensor live data area:
This captures the sensor current response for 5 oscillation waves. This can be useful when studying the measurements being employed and for troubleshooting the system if it is not operating correctly:
NOTE: The sample rate for the capture is 2.56Mhz at 16 bits, so 1.28MB of data is transferred over CAN then saved as a comma delimited ASCII file (approximately 10MB in size) so this operation can take 3-‐4 minutes.
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Sensor Details NOxTrac sensors are simple in concept. Au and Pt electrodes with a porous electrolyte (YSZ) cover on top of an alumina substrate with an embedded printed Pt heater:
However, these ‘proof of concept’ elements are not perfect in execution. They are co-‐fired, but the YSZ and alumina are poorly matched both in terms of dynamic and final shrinkage, so the elements are warped:
And have micro-‐cracks in the electrolyte and alumina as fabricated:
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Scanning electron image above at 65x magnification shows cross-‐section of element with YSZ electrolyte, gold electrode, and via on top of the alumina. These cracks tend to become worse with thermal cycles and thermal stress, which is why the sensor warmup and cooldown is presently very slow:
Optical image above shows YSZ electrolyte surface treated with dye to highlight extent of crack growth after aggressive thermal cycling. We are working on a better matched material set. Please contact us to get the latest status. In addition to the cells being mechanically imperfect, signal response is also compromised for a simple construction. The electrodes are connected using Pt filled vias inside the cell (like on a printed circuit board):
Optical image above shows cross-‐section of an element. Because of the stress on the cell (warpage) and because of excess sintering aids in the alumina tape used for the substrate, these Pt filled vias pass through dense YSZ. This diminishes response to NO by approximately 1/3 or 1/4. The point is not to make excuses for the performance of these probes, but to simply explain. We developed these imperfect probes to demonstrate that a very simple probe, even with defects, could be operated in a real vehicle environment using a very simple measurement strategy and still provide meaningful data.
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These probes have met that goal:
Above data are from the final 200 seconds of the hot start 505 transient during the FTP-‐75 drive cycle and indicate the potential of the probe for operation in real vehicle operation. However, if you would like to examine the overall technology more closely we would recommend looking at a different manifestation. We can provide ‘furnace cells’, which are just the electrodes in the electrolyte and free of ceramic defects. These cells give a much better idea of how much signal can be achieved, how other gas species can potentially be extracted, and the overall stability of our measurement method.
POC$6&H20A$15&NOxTrac&sensor& POC$6&H20A$15&NOxTrac&sensor&
Commercial&NOx&sensor& Commercial&NOx&sensor&
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Interpreting Measurements Measurement Basics The proof of concept cells included with this kit are operated using a very simple implementation of our technology and measurement principle. As previously noted, the objective was to prove the viability of a low cost, simple system in a vehicle environment. The cell is excited using a 20 Hz triangle wave with bursts of 20 kHz sine waves embedded at the triangle wave peaks:
The signal is scaled down so that it is +/-‐ 100 mV when it reaches the sensor. The embedded sine waves are inverted top/bottom:
This makes excitation symmetric.
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However, if you look at the captured waveform you can see that the current response of the cell is not at all symmetric:
The cell displays a distinct polarity and a surprisingly complex wave shape. By matching frequency and excitation wave shape many interesting relationships between different gas species can be found. However, these proof of concept elements have a relatively low optimum operating frequency for detecting NO -‐ approximately 3-‐5 Hz (we have constructed other prototype geometries with optimum NO detection frequency as high as 50 Hz). In order to be responsive enough to hold temperature and take measurements in a diesel pickup truck we are operating the cell about 4x faster than optimum. This both sacrifices some NO response and somewhat limits our measurement choices. Because of our compromises for measurement speed these proof of concept systems are primarily driven by three simple measurements. The first two are time based:
On each side of the wave we measure time from the start of ½ the excitation wave until the sensor reaches zero current.
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The third measurement is the amplitude of the current peaks achieved during the 20 kHz sine wave:
These measurements were also selected because they are relatively simple and low cost to implement in hardware. The time measurements for zero current crossing are made with a timer in the processor and an analog comparator. The high frequency peaks are measured with a high pass filter and sample and hold techniques. Transfer Function Basics For more details on our exact transfer function used in this system and variants that can be used with other NOxTrac™ cells, please contact us. But the basics can be explained just by examining the two measured time signals described above:
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In the graph above O2 concentration is shown at three steps, 5%, 10.5%, and 15%. At each step NO is added (ppm: 0, 5, 10, 25, 50, 100, 0). CBhi (Comparator B, hi side) responds to both O2 and NO. CBlo (Comparator B, lo side) responds to NO at a lower ratio to O2. The transfer function for this system is relatively simple:
-‐ Convert both time measurements to calibrated O2 measurements -‐ Treat the difference between the O2 measurements as a NO error which we correct
CBlo with -‐ Subtract the corrected CBlo O2 from CBhi -‐ Calculate NO from the remaining CBhi signal
We do not currently correct for temperature deviations, but that information is available from the DC amplitude of the 20 kHz current peaks. That measurement is used to feed the PID loop controlling the heater.
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All Logged Measurements Log Files contain the following data columns for all connected modules: Name Units Description Time Seconds Common column used by all modules, 50 mS
increments Status Bits Operational Status of the Module Heat_Pct % Duty cycle of heater in percentage Heat_Pwr Watts Calculated Heater Power using current,
voltage, and duty cycle ACz_Delta+++ ADC Counts Average DC amplitude of 20 kHz current
peaks ACz_Max ADC Counts Average high DC peak of high 20 kHz
injection ACz_Min ADC Counts Average low DC peak of high 20 kHz injection ACz_Max_LO ADC Counts Average high DC peak of low 20 kHz injection ACz_Min_LO ADC Counts Average low DC peak of low 20 kHz injection X0hi* 1/2.56M Sec Digital zero crossing measurement hi side X0lo* 1/2.56M Sec Digital zero crossing measurement lo side CBhi 1/84M Sec Comparator zero crossing measurement hi
side NOxO2raw 1/84M Sec CBhi after simple moving average filter CBlo 1/84M Sec Comparator zero crossing measurement lo
side O2raw 1/84M Sec CBlow after simple moving average filter +++ Used for PID control of the heater *These measurements can be moved for extracting more signal or other gas species. Noise and Filtering These proof of concept cells are significantly noisier than other furnace and prototype cells that we have previously shown in presentations. In those samples raw data is generally shown with either no filtering or 1 second averaging. The primary reasons for this noise are twofold. First, we are using simple Pulse Width Modulated (PWM) negative side switching for heater control. This, combined with the relatively poor insulation properties of the alumina tape we are using, creates spikes, which can be seen in the captured waveform:
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Second, the micro cracks in the electrolyte at the Au electrode interface appears to make these cells more susceptible to EMI/RF:
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Presently we are only using software filtering. Please note, the following graphs are all 0, 5, 10, 25, 50, 100, 0 ppm NO. The raw signals are recorded:
A moving average is generated for the chart displays and recorded:
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The transfer function uses a Finite Impulse Response filter (Matlab script available):
In addition to working on improving the raw signal (eliminating micro cracks and lowering the Na content of the alumina substrate for better electrical insulation properties) we are working with an OEM later this summer to evaluate filter tradeoffs with a broader range of real world vehicle data.
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Appendix A – Notes Regarding Sensor Drift Because these proof of concept cells have ceramic defects as fabricated, they have non-‐trivial drift. Most samples are stable enough for one or two days of testing, but the ever-‐worsening cracking causes their bulk impedance to keep increasing. Because we use bulk impedance to maintain temperature, the operating temperature continues to drift upward. This both diminishes cell sensitivity and speeds up further cracking. Obviously, producing defect free cells would greatly help this situation. However, we believe that ALL heated sensor elements will drift over the operational life of the sensor. This means that the techniques we have been developing to ‘free air’ re-‐calibrate these sensors will potentially be applicable to even production grade sensors. Current Approach: We currently flow free air (20.95% O2) over the sensors and move cell temperature up and down a fixed amount in cell real impedance. This provides us a measurement of any offset in O2 response and the change (if any) in the amplitude of the response (gain). You can trigger this test with the evaluation tool. Flow free air, start a log, and press the “Heater Cal” button just below the Sensor Module Status area:
The downside to this approach is that changing cell temperature even just a few degrees C and waiting for stability is relatively slow. In an operational vehicle we believe that a free air calibration needs to take no more than 1-‐2 seconds to be viable. Under Development: If you examine our cells using a lab potentiostat you will observe that our response to O2 also changes with frequency. We are currently trying to develop an approach to use this aspect of cell behavior to do free air calibration at the normal, fixed, operating temperature. We believe that this approach would be fast enough to periodically use in a vehicle environment.
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Appendix B – CAN Protocol If you would like to operate and monitor the modules and sensors without using our evaluation tool the CAN protocol used is available in a separate document upon request.