DATASHEET SEARCH SITE | WWW.ALLDATASHEET.COM

Document overview

  • Manufacturer or author: Provided By ALLDATASHEET.COM(FREE DATASHEET DOWNLOAD SITE)
  • PDF pages: 5

Technical content

information and/or support, visit www.analog.com/CN0216. Fax: 781.461.3113 ©2011 Analog Devices, Inc. All rights reserved. resolution for a load cell with a full-scale output of 10 mV . that operate at various low speeds. Figure 1. Weigh Scale System Using the AD7791 (Simplified Schematic, All Connections and Decoupling Not Shown)

Figure 3. AD7791 RMS Noise for Different Output Data Rates and a 2.5 V without the load cell or the input amplifier connected. system. In addition, the load cell itself will add noise.

3.75 V p-p signal into the ADC, which is approximately 38% of

Figure 4. Measured Output Code for 500 Samples Showing counts at the expense of a reduced data rate.

Figure 5. Measured Histogram for 500 Samples Showing The AD7171 is a 16-bit sigma-delta ADC. For a lower power consumption solution, use the ADA4051-2. only 20 µA of supply current per amplifier.

  • PC with a USB port and Windows XP or Windows Vista (32-bit), or Windows 7 (32-bit)
  • E VA L-CN0216-SDPZ circuit evaluation board
  • E VA L-SDP-CB1Z SDP evaluation board
  • CN0216 evaluation software
  • Tedea-Huntleigh 505H-0002-F070 load cell or equivalent
  • Power supply: +6 V, o r + 6 V “wall wart” Getting Started Load the evaluation software by placing the CN0216 Evaluation Software disc in the CD drive of the PC. Using My Computer, locate the drive that contains the evaluation software disc and open the Readme file. Follow the instructions contained in the Readme file for installing and using the evaluation software. Functional Block Diagram See Figure 1 of this circuit note for the circuit block diagram, and the PDF file “E VA L-CN0216-SDPZ-SCH” for the circuit schematics. This file is contained in the CN0216 Design Support Package. Setup Connect the 120-pin connector on the E VA L-CN0216-SDPZ circuit board to the connector marked “CON A” on the E VA L-SDP-CB1Z evaluation (SDP) board. Nylon hardware should be used to firmly secure the two boards, using the holes provided at the ends of the 120-pin connectors. Connect the load cell the E VA L-CN0216-SDPZ board. With power to the supply off, connect a +6 V power supply to the pins marked “+6 V” and “GND” on the board. If available, a +6 V "wall wart" can be connected to the barrel jack connector on the board and used in place of the +6 V power supply. Connect the USB cable supplied with the SDP board to the USB port on the PC. Note: Do not connect the USB cable to the mini USB connector on the SDP board at this time. Test Apply power to the +6 V supply (or “wall wart”) connected to E VA L-CN0216-SDPZ circuit board. Launch the evaluation software and connect the USB cable from the PC to the USB mini-connector on the SDP board. The software will be able to communicate to the SDP board if the Analog Devices System Development Platform driver is listed in the Device Manager. Once USB communications are established, the SDP board can now be used to send, receive, and capture serial data from the E VA L-CN0216-SDPZ board. Information and details regarding how to use the evaluation software for data capture can be found in the CN0216 Evaluation Software Readme file. Information regarding the SDP board can be found in the SDP User Guide. Analyzing the Data At least 500 samples of the ADC output data should be taken. Once the sample set is exported to a spreadsheet program, such as Excel, the samples can be analyzed. The standard deviation of the samples is approximately equal to the rms noise, assuming a Gaussian noise distribution. The peak-to-peak noise is approximately equal to the rms value multiplied by 6.6. The peak-to-peak noise can also be taken directly from the sample set by simply taking the difference between the largest and smallest sample. In practice, the results obtained using this

Rev. 0 | Page 5 of 5 method were approximately the same as the value obtained by multiplying the rms value by 6.6. The values obtained from the sample set are in LSBs, so they must be converted into voltage, where 1 LSB = 0.596 µV for a 5 V reference. If desired, the results of several sample sets can be averaged to get a more accurate measurement. Noise-free code resolution is calculated from the peak-to-peak noise as described previously in this circuit note. LEARN MORE Kester, Walt. 1999. Sensor Signal Conditioning. Section 2. An alog Devices. Kester, Walt. 1999. Sensor Signal Conditioning. Section 3. Analog Devices. Kester, Walt. 1999. Sensor Signal Conditioning. Section 4. Analog Devices. MT-004 Tutorial, The Good, the Bad, and the Ugly Aspects of ADC Input Noise—Is No Noise Good Noise? Analog Devices. MT-022 Tutorial, ADC Architectures III: Sigma-Delta ADC Basics, Analog Devices. MT-023 Tutorial, ADC Architectures IV: Sigma-Delta ADC Advanced Concepts and Applications, Analog Devices. MT-031 Tutorial, Grounding Data Converters and Solving the Mystery of "AGND" and "DGND", Analog Devices. MT-063 Tutorial, Basic Three Op Amp In-Amp Configuration, Analog Devices. MT-101 Tutorial, Decoupling Techniques, Analog Devices. Wong, Vicky, AN-1114 Application Note, Lowest Noise Zero- Drift Amplifier Has 5.6 nV/√Hz Voltage Noise Density, Analog Devices. CN-0102 Circuit Note, Precision Weigh Scale Design Using the AD7190 24-Bit Sigma-Delta ADC with Internal PGA, Analog Devices. CN-0107 Circuit Note, Weigh Scale Design Using the AD7780 24-Bit Sigma-Delta ADC with Internal PGA, Analog Devices. CN-0108 Circuit Note, Weigh Scale Design Using the AD7781 20-Bit Sigma-Delta ADC with Internal PGA, Analog Devices. CN-0118 Circuit Note, Precision Weigh Scale Design Using the AD7191 24-Bit Sigma-Delta ADC with Internal PGA, Analog Devices. CN-0119 Circuit Note, Precision Weigh Scale Design Using the AD7192 24-Bit Sigma-Delta ADC with Internal PGA, Analog Devices. CN-0155 Circuit Note, Precision Weigh Scale Design Using a 24- Bit Sigma-Delta ADC with Internal PGA and AC Excitation, Analog Devices. Data Sheets and Evaluation Boards AD7791 Data Sheet ADA4528-1 Data Sheet ADP3301 Data Sheet CN-0216 Circuit Evaluation Board (EV AL-CN0216-SDPZ) System Demonstration Platform (EV AL-SDP-CB1Z)

REVISION HISTORY

9/11—Revision 0: Initial Version (Continued from first page) Circuits from the Lab circuits are intended only for use with Analog Devices products and are the intellectual property of Analog Devices or its licensors. While you may use the Circuits from the Lab circuits in the design of your product, no other license is granted by implication or otherwise under any patents or other intellectua l property by application or use of the Circuits from the Lab circuits. Information furnished by Analog Devices is believed to be accurate and reliable. However, "Circuits from the Lab" are supplied "as is" and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of mer chantability, noninfringement or fitness for a particular purpose and no responsibility is assumed by Analog Devices for their use, nor for any infringements of patents or other rights of third parties that may result from their use. Analog Devices reserves the right to change any Circuits from the Lab circuits at any time without notice but is under no obligation to do so. ©2011 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. CN10164-0-9/11(0)