# Digital Diagnostics

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## Open Circuit and Overcurrent Diagnostic Response Time

 Open circuit 145 µs Overcurrent 145 µs

To calculate open circuit diagnostic response times when using test pulses, use the following equation:

Open circuit diagnostic response time (with test pulses) = Test pulse width + Test pulse constant + 295 µs

• Test pulse width is a user-configurable parameter in the Functional Safety Editor.
• Use the following table to determine the test pulse constant based on test pulse width.

To calculate overcurrent diagnostic response times when using test pulses, use the following equation:

Overcurrent diagnostic response time (with test pulses) = Test pulse width + Test pulse constant + 295 µs

• Test pulse width is a user-configurable parameter in the Functional Safety Editor.
• Use the following table to determine the test pulse constant based on test pulse width.
Table 1. Test Pulse Constant
Test Pulse Width Test Pulse Constant
≤16,384 µs 1 µs
≥16,500 µs 125 µs

## Test Pulse Diagnostic Response Time

Use the following equation to calculate test pulse diagnostic response times.

Test pulse diagnostic response time = Test pulse period

• Test pulse period is a user-configurable parameter in the Functional Safety Editor.
• For more information on determining the test pulse period, refer to the Test Pulses section.

## Discrepancy Diagnostic Response Time

Use the following equations to calculate discrepancy diagnostic response times.

Discrepancy diagnostic response time (0 to 1)

Discrepancy diagnostic response time = Discrepancy time + Discrepancy constant + Debounce filter time + Debounce constant + 18 µs

Discrepancy diagnostic response time (0 to 1) with test pulses configured:

Discrepancy diagnostic response time = (2 × Debounce filter time) + (3 × Debounce constant) + Discrepancy time + Discrepancy constant + Test pulse width + 39 µs

Discrepancy diagnostic response time (1 to 0) with or without test pulses configured

Discrepancy diagnostic response time = Input discharge time + Discrepancy time + Discrepancy constant + Debounce filter time + Debounce constant + 15 µs

• Discrepancy time, debounce filter time, and test pulse width are user-configurable parameters in the Functional Safety Editor.
• For more information about determining the debounce filter time when using test pulses, refer to the Filter Times for Test Pulses section.
• For more information on configuring discrepancy times, refer to the Discrepancy Diagnostics for Digital Inputs section.
• Use the following table to determine the discrepancy constant based on discrepancy time.
Table 2. Discrepancy Constant
Discrepancy Time Discrepancy Constant
100 µs ≤ discrepancy time ≤ 16,383 µs 2 µs
16,500 µs ≤ discrepancy time ≤ 2,047.875 ms 126 µs
2,125 ms ≤ discrepancy time ≤ 30 s 126 ms
Note

You cannot set discrepancy time to 0 µs when using dual input or dual input with test pulse.

• Use the following table to determine the debounce constant based on debounce filter time.
Table 3. Debounce Constant
Debounce Filter Time Debounce Constant
0 µs < debounce filter time ≤ 16,383 µs 2 µs
16,500 µs ≤ debounce filter time ≤ 2,047.875 ms 126 µs
2,125 ms ≤ debounce filter time ≤ 5 s 126 ms
Note

You cannot set debounce filter time to 0 µs when using dual input with test pulse.

For single and dual output configurations, use the following times.

Very light

150 µs

Light

1,100 µs

Medium

11,025 µs

Heavy

110,150 µs

For single outputs configured with external readback, use the following equations to calculate readback diagnostic response times based on output line load.

Table 4. Readback Diagnostic Response Time Equations
Very light Debounce filter time + Debounce constant + Readback delay + Readback constant + 61 µs
Light Debounce filter time + Debounce constant + Readback delay + Readback constant + 1,021 µs
Medium Debounce filter time + Debounce constant + Readback delay + Readback constant + 10,021 µs
Heavy Debounce filter time + Debounce constant + Readback delay + Readback constant + 100,145 µs
• Debounce filter time, readback delay, and output line load are user-configurable parameters in the Functional Safety Editor.
• Use the following table to determine the debounce constant based on the debounce filter time.
Table 5. Debounce Constant
Debounce Filter Time Debounce Constant
0 µs < debounce filter time ≤ 16,383 µs 2 µs
16,500 µs ≤ debounce filter time ≤ 2,047.875 ms 126 µs
2,125 ms ≤ debounce filter time ≤ 5 s 126 ms
• Use the following table to determine the readback constant based on the readback delay.