| Step 1: Measure resistance on the H1 segment conductors at the removed connector coming in from the field. | |
| Measure resistance from the: | Expected result: |
| + signal conductor to - signal conductor | > 50 K ohms (increasing)
This value will change due to the capacitor charging in the termination RC circuit and the capacitance in the fieldbus cables. |
| + signal conductor to drain/shield wire | open circuit >20 MΩ |
| - signal conductor to drain/shield wire | open circuit > 20 MΩ |
| + signal conductor to instrument ground bar | open circuit > 20 MΩ |
| - signal conductor to instrument ground bar | open circuit > 20 MΩ |
| drain/shield wire to instrument ground bar | open circuit > 20 MΩ |
| Step 2: Measure capacitance on the H1 segment conductors at the removed connector coming in from the field. | |
| Measure capacitance from the: | Expected result: |
| + signal conductor to - signal conductor | 1 µF (0.80 to 1.20 µF acceptable)
A reading of <.5 µF indicates no terminator on the segment. A
reading of a nominal 2 µF indicates a second terminator on the segment. The
acceptable values assume that the power supply terminator is used as the second
terminator and only one additional terminator is connected in the field.
Otherwise, the expected result would be 2 µF.
Note The values for this measurement will be invalid on the Pepperl+Fuchs FieldConnex® Field Barrier for I.S. applications. The Pepperl+Fuchs FieldConnex® Field Barrier is an Emerson Alliance Program product. |
| + signal conductor to drain/shield wire | < 300 nF |
| - signal conductor to drain/shield wire | < 300 nF |
| + signal conductor to instrument ground bar | < 300 nF
An actual reading that is much greater or varies in a capacitor charging manner to a high capacitance value (>1 µF) indicates a poor quality noisy ground on the shield ground bar. Be sure to correct this ground problem to prevent communication errors on the fieldbus segment. A reading of 300 nF indicates noise on the ground system. Field data has shown that readings of up to 500 nF can be acceptable providing the fieldbus signal waveform and voltage compare to that shown in the sample waveform with two terminators and 1000 feet of cable. Refer to Sample waveforms for information. |
| - signal conductor to instrument ground bar | < 300 nF
An actual reading that is much greater or varies in a capacitor charging manner to a high capacitance value (>1 µF) indicates a poor quality noisy ground on the shield ground bar. Be sure to correct this ground problem to prevent communication errors on the fieldbus segment. A reading of 300 nF indicates noise on the ground system. Field data has shown that readings of up to 500 nF can be acceptable providing the fieldbus signal waveform and voltage compare to that shown in the sample waveform with two terminators and 1000 feet of cable. Refer to Sample waveforms for more information. |
| drain/shield wire to instrument ground bar | < 300 nF
An actual reading that is much greater or varies in a capacitor charging manner to a high capacitance value (>1 µF) indicates a poor quality noisy ground on the shield ground bar. Be sure to correct this ground problem to prevent communication errors on the fieldbus segment. A reading of 300 nF indicates noise on the ground system. Field data has shown that readings of up to 500 nF can be acceptable providing the fieldbus signal waveform and voltage compare to that shown in the sample waveform with two terminators and 1000 feet of cable. Refer to Sample waveforms for more information. |
| Step 3: Verify the terminator switch. | |
| Procedure | Expected result |
| Verify if the power supply has a terminator switch. Switch On or Off depending upon application. | 2 terminators total per segment |
| Verify if the device connection block has a terminator switch. Switch On or Off depending upon application. | 2 terminators total per segment |
| Step 4: Measure DC voltage at the connector going to the field. | |
| Procedure | Expected result |
|
Reconnect the previously removed terminal block connectors to the power supply. Measure the output DC voltage at the power supply terminals and verify that the voltage is appropriate for the fieldbus power supply installed. |
|
| Step 5: Measure the AC waveform at the connector going to the field. | |
| Procedure | Expected result |
| Set the scope to AC, 200 mV/division, 10 micro seconds/division for best results and press HOLD to capture the waveform | 500 mV and 900 mV peak to peak |
| Verify the waveform against the expected waveform shown in Sample waveforms. Note the differences in the signals with 1 terminator and with 3 terminators . | |