Table Of Contents

Output Line Load

Version:
    Last Modified: September 6, 2017

    You can set the line load for digital outputs or digital inputs with test pulses.

    Figure 1. Output Line Load

    Setting an appropriate output line load is necessary for test pulse and readback diagnostics. Heavy output line loads work for all applications within module specifications but will result in slower response times. Reducing output line loads will enable shorter test pulses, readback delays, and faster response times.

    There are two ways to set output line load:

    • Calculate the discharge time using the following equation and the Output Line Load for Input Discharge Times table.
    • Approximate the discharge time based on the configuration, external load, cable length and capacitance using the Output Line Load Recommendations table.

    t = R × ( C + 600 p F ) × ln ( R × 0.8 m A + 5.7 V R × 0.8 m A + 30 V )

    Table 1. Output Line Load Discharge Times
    Input Discharge Time Output Line Load
    Discharge time < 40 µs Very Light
    40 µs < discharge time < 1,000 µs Light
    1,000 µs < discharge time < 10,000 µs Medium
    10,000 µs < discharge time < 100 ms Heavy
    Table 2. Output Line Load Recommendations
    Configuration External Load[1] Cable Length/Capacitance Output Line Load
    • Single output
    • Dual output
    • Single output with internal test pulse
    • Dual output with internal test pulse
    High Impedance ≤10 m and ≤1.8 nF Light
    High Impedance ≤50 m and ≤9 nF Medium
    High Impedance >50 m Heavy
    ≤3 kΩ ≤10 m and ≤1.8 nF Very Light
    ≤3 kΩ ≤50 m and ≤9 nF Light
    ≤3 kΩ >50 m Medium
    • Single output with external test pulse
    • Dual output with external test pulse
    • Single output with external readback
    • Single input with test pulse
    • Dual input with test pulse
    >3 kΩ ≤50 m and ≤9 nF Light
    >3 kΩ >50 m Medium
    ≤3 kΩ ≤50 m and ≤9 nF Very Light
    ≤3 kΩ >50 m Medium
    • 1 When the output load on the DO channel is a DI channel on the same module, load is >3 kΩ.

    Recently Viewed Topics