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

3.4.3 Carrier Start and Stop Transient Tests

The next test is the carrier start and stop transient measurements. The test setup in Figure 3-11 is similar to the previous test where the carrier start and stop are measured. In this test setup, an HCF_TOOL-32 filter is measured by another channel of the oscilloscope. This low-pass filter removes the higher-frequency HART signal band and passes any signal below 25Hz. The filtered signal shows the current measurement of the primary variable. This test verifies that the HART transmission start and stop does not create any noise that interferes with the primary variable measurement.

HART Carrier Start and Stop Time Test Setup Figure 3-11 HART Carrier Start and Stop Time Test Setup

Figure 3-11 shows the oscilloscope plots of the HART signal while being enabled and disabled. Additionally, the oscilloscope measures the same signal filtered through the HCF_TOOL-32. The HCF_TOOL-32 is capacitively coupled to the resistive load. The low-pass filtered signal in blue shows the output noise amplitude of the transmitter. Here, the specification requires a peak amplitude of 100mV maximum. The transmitter maximum shows a 22.1mVP-P noise amplitude for the transition noise. Table 3-3 reports the results of the scope measurements.

HART Carrier Start and Stop Time Transient Test Oscilloscope Results Figure 3-12 HART Carrier Start and Stop Time Transient Test Oscilloscope Results
Table 3-3 Carrier Start and Stop Measurement Results Filtered Through an HCF_TOOL-32
TEST MEASUREMENT MAXIMUM RESULT
Carrier start peak analog filter output 21.8mVPP 100mVPP Pass
Carrier stop peak analog filter output 22.1mVPP 100mVPP Pass