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

3.4.7 Noise Sensitivity Test

The transmitter is also tested for the HART transmission in the presence of noise at different frequencies. For this test, a signal generator varies the supply voltage at different magnitudes and frequencies to simulate noise.

The noise sensitivity test verifies that the HART signal is received despite having out-of-band noise, and even some low-signal in-band noise. Figure 3-19 shows the test setup for the HART noise sensitivity test.

Noise Sensitivity Test Figure 3-19 Noise Sensitivity Test

The signal generator is set to frequencies and amplitudes to mimic noise during a HART transmission. There are five frequency and amplitude combinations used for this test. Table 3-7 lists the different frequency and amplitude combinations used for the signal generator to simulate the noise.

Table 3-7 Measured Data from the Noise Sensitivity Test
TYPE OF INTERFERENCE FREQUENCY LEVEL NUMBER OF MISSED COMMAND ERRORS RESULT
In band 1700Hz 55mVPP 0 Pass
Out of band 250Hz 220mVPP 0 Pass
Out of band 125Hz 880mVPP 0 Pass
Out of band 63Hz 3.52VPP 0 Pass
Out of band 29Hz 16VPP 0 Pass

While the signal generator is active, the HART test system sends 100 consecutive commands to the transmitter. The transmitter sends a response to the commands. Any missed command or interrupted transmission is considered an error.