UltimaSerial What is Analog Calculated Trigger Mode in Data Acquisition?
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Besides letting you stabilize repeating waveforms in an oscilloscope-like display, analog trigger mode in data acquisition is especially important to study sudden (single-shot) change of an analog signal

What are the traditional analog trigger modes?

In traditional data acquisition devices, one can find the following common analog trigger modes:

  1. Rising edge trigger mode, which is also called positive slope trigger: Trigger happens when the signal passes a trigger level while it is rising
  2. Falling edge trigger mode, which is also called negative slope trigger: Trigger happens when the signal passes a trigger level while it is falling
  3. Above Level trigger mode: Trigger happens simply when the signal is above a trigger level
  4. Below Level trigger mode: Trigger happens simply when the signal is below a trigger level

On top of these, features like pre-trigger length, post-trigger length and hysteresis are added.

Problems with traditional trigger modes

Case 1: Take a look at Analog Derivative Trigger Mode

Case 2: We want to trigger when the power consumption exceed 100W, where the power is derived from the reading of a voltage measurement and a current measurement

This trigger relies on two parameters and none of the traditional analog trigger modes can do it.

Case 3: We want to trigger when the temperature is above 100C or below 4C

Bad news, this is a double triggering and none of the traditional analog trigger modes can do it, either

Our Answer

The answer is in Analog Calculated Trigger Mode.

With Analog Calculated Trigger Mode, the trigger condition can have multiple parameters, multiple trigger levels, even readings in different time!

The power of Analog Calculated Trigger Mode

  • Operators include: +, -, *, /, ^, %, &, |, !, >, >=, <, <=, !=, ==

  • Functions include: abs, floor, hex, round, if, avg, bin, log, sqrt, ceil, log10, sum, max, min, acos, asin, atan, sin, sinh, cos, tan, cosh, tanh

  • To use the reading from a channel, use #n. For example, #0 is the reading from the first enabled channel in Windaq

  • To access the sample rate, use #@. 

  • You can use earlier readings to form a more complicated math expression. To do so, add a letter after #, and alphabet order of the letter represents the delay, such as:

    • #0 is the reading from channel 0

    • #A0 is the reading from channel 0, one scan earlier

    • #B1 is the reading from channel 1, two scans earlier

    • Readings from up to 26 scans earlier can be used, for example, #Z0.

    • For example: use ( #0-#A0)*#@, or  #0-#A0, to form a two-point derivative

Case Solution:

Case 1: Take a look at the great example in Analog Derivative Trigger Mode

Case 2: We can trigger on ( #0*#1)>100, where Channel 0 reads the voltage in terms of Volt and Channel 1 reads the current in turns of Amp

Case 3: We can trigger on #0>100 | #<5, where channel 0 reads the temperature in terms of C

Last update: 02/24/12

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