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Common sources of measurement error in LED production testing include lead resistance, leakage current, electrostatic interference, and light interference, but junction self-heating is one of the most significant error sources. The two tests susceptible to junction heating are the forward voltage and leakage current tests. As the junction heats, the voltage will drop or, more importantly, the leakage current will increase during the constant voltage test. Therefore, it is important to shorten the test time as much as possible without sacrificing measurement accuracy or stability.

LED生产测试中的常见测量误差源[1]包括引线电阻[2]、漏电流、静电干扰和光干扰[3]，但是结自热[4]是最重要的误差源之一。对结发热最敏感的两种测试是正向电压测试和漏电流测试。当半导体结发热时，电压将会下降，更重要的是，在恒压测试过程中漏电流会增大。因此，在不影响测量精度或稳定性的情况下尽可能缩短测试时间是非常重要的。

Smart instruments with onboard test script engines simplify configuring the device soak time before the measurement, as well as the amount of time the input signal is acquired. The soak time allows any circuit capacitance to settle before the measurement begins. The measurement integration time is determined by the number of power line cycles (NPLC). If the input power were at 60Hz, a 1NPLC measurement would require 1/60th of a second or 16.667ms. The integration time defines how long the A-to-D converter acquires the input signal, and it represents a trade-off between speed and accuracy.

具有板载测试脚本引擎[5]的智能仪器能够简化配置测量前器件的保温时间（soak time）以及采集输入信号的时间。在保温时间内所有的电路电容在测量开始前稳定下来。测量积分时间（integration time）取决于电源线周期数（NPLC）。如果输入电源是60Hz，那么1NPLC测量就需要1/60秒，即16.667ms。积分时间决定了A/D转换器采集输入信号的时间，它要在测量速度和精度之间进行折中。

Typical soak times for the V_F test are from less than a few hundred microseconds to five milliseconds, and from five to 20 milliseconds for the I_L test. By using these short test times, errors due to the junction heating are reduced. Also, the junction heating characteristics can be determined by performing a series of tests and only varying the test time.

V_F测试的典型保温时间从不到几百微秒到5毫秒，I_L测试的保温时间从5到20毫秒。通过利用这些极短的测试时间，就能够减少由于结发热导致的误差。此外，通过执行一系列测试并只检验测试时间，可以对结发热的特征进行分析。

To further reduce test time and junction self-heating, Series 2600A instruments are capable of pulsed operation. In this mode, they can source their outputs precisely for a specified period. Pulse width resolution of one microsecond gives precise control over how long power is applied to the device. Pulsed operation also allows these instruments to output current levels well beyond their DC capabilities. For example, the Model 2602A can output 3A DC at 6V. In pulsed mode, it can output 10A at 20V.

为了进一步缩短测试时间，减少结自热效应，2600A系列仪器支持脉冲操作[6]。在这种模式下，它们能够在指定的周期内在输出端产生精密的信号源。1微秒的脉宽分辨率能够精确控制器件的加电时间。这类仪器在脉冲操作模式下还能够输出大大超出其直流能力的电流值。例如，2602A在6V下能够输出3A的直流电流。而在脉冲模式下，它能够在20V下输出10A的电流。

[1] 误差源：http://www.keithley.com.cn/llm/a/9.html

[2] 引线电阻：http://www.keithley.com.cn/products/localizedproducts/localizedproducts/2004_china_catalog.pdf

[3] 静电干扰：http://www.keithley.com.cn/llm/a/22.html

[4] 自热：http://www.keithley.com.cn/news/prod110414

[5] 脚本引擎：http://www.keithley.com.cn/news/prod080923

[6] 脉冲测试：http://www.keithley.com.cn/news/prod061121