SLAAEH8 October   2024 AFE781H1 , AFE782H1 , AFE881H1 , AFE882H1 , DAC8740H , DAC8741H , DAC8742H

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 The 4-20mA Loop
    2. 1.2 The HART Protocol
      1. 1.2.1 Adding HART to the 4-20mA Loop
      2. 1.2.2 HART FSK
  5. 2AFE881H1 HART Modem
    1. 2.1 AFE881H1 HART Transmitter
    2. 2.2 Detailed Schematic
      1. 2.2.1 Input Protection
      2. 2.2.2 Startup Circuit
      3. 2.2.3 Voltage-to-Current Stage
      4. 2.2.4 Voltage-to-Current Calculation
      5. 2.2.5 HART Signal Transmission
      6. 2.2.6 HART Input Protection
      7. 2.2.7 Current Consumption
      8. 2.2.8 HART Transmitter Board
      9. 2.2.9 HART Protocol Stack
  6. 3HART Testing and Registration
    1. 3.1  HART History and the FieldComm Group
    2. 3.2  HART Testing Overview
      1. 3.2.1 HART Protocol Specifications
      2. 3.2.2 HART Protocol Test Specifications
      3. 3.2.3 Remote Transmitter Device Testing
    3. 3.3  HART Test Equipment
    4. 3.4  HART Physical Layer Testing
      1. 3.4.1 FSK Sinusoid Test
      2. 3.4.2 Carrier Start and Stop Time Tests
      3. 3.4.3 Carrier Start and Stop Transient Tests
      4. 3.4.4 Output Noise During Silence
      5. 3.4.5 Analog Rate of Change Test
      6. 3.4.6 Receive Impedance Test
      7. 3.4.7 Noise Sensitivity Test
      8. 3.4.8 Carrier Detect Test
    5. 3.5  Data Link Layer Tests
      1. 3.5.1 Data Link Layer Test Specifications
      2. 3.5.2 Data Link Layer Test Logs
    6. 3.6  Universal Command Tests
    7. 3.7  Common-Practice Command Tests
    8. 3.8  Device Specific Command Tests
    9. 3.9  HART Protocol Test Submission
    10. 3.10 HART Registration
  7. 4Other TI HART Modem Designs
  8. 5Summary
  9. 6Acknowledgments
  10. 7References

3.4.4 Output Noise During Silence

Similar to the previous test, this test measures the HART signal band through a filter. Here, the HCF_TOOL-31 filter is used. This filter is a 500Hz to 10kHz bandpass filter that allows all of the in-band HART signal through. The test is devised to view the noise when the HART signal is inactive and verify there is no in-band noise that can be received as a HART signal in error. Figure 3-13 shows the test setup for the output noise during silence.

HART Output Noise During Silence Test Setup Figure 3-13 HART Output Noise During Silence Test Setup

Figure 3-14 shows the oscilloscope shot of the measurement of the output noise during silence. This shows the inactive HART signal at the top of the oscilloscope plot after the HART has been disabled. The middle trace in the plot shows the same signal filtered through the HCF_TOOL-31, showing the in-band noise for the primary variable. The bottom trace of the oscilloscope plot is the RTS which is high indicating the HART is inactive. Table 3-4 shows the results of the noise measured during silence.

Output Noise During Silence Oscilloscope Test Figure 3-14 Output Noise During Silence Oscilloscope Test
Table 3-4 Output Noise During Silence Test Results
TEST MEASUREMENT MAXIMUM RESULT
Broadband noise without filter 2.08mVRMS 138mVRMS Pass
In-band noise using HCF_TOOL-31 bandpass filter 3.23RMS 22mVRMS Pass