Trigger Parameters

The above toolbar contains (from left to right):

Trigger Mode, Trigger Source, Trigger Edge, Trigger Level, and Trigger Delay.

For data acquisition, it is possible to specify a trigger condition for collecting a frame of data. There are two concurrent processes in this context, one is data sampling and collecting, the other is data analysis and display. Once a frame of data is collected into the PC memory, the software will start immediately to search for the next trigger event in order to collect the next frame of data. Meanwhile, the collected data will be analyzed and then displayed. With the fast PCs nowadays, normally data analysis and display will take less time than data sampling and collecting as the latter one is constrained by the scan time and cannot benefit from the fast speed of the PCs. In case that the data sampling and collecting process is faster than the data analysis and display process, the latest frame of data will overwrite the previous one even if it has not yet been analyzed and displayed. This is to ensure that data analysis and display will always be performed on the latest collected frame of data.

In order to obtain a stable display for a periodic signal, the trigger parameters must be set properly such that there is only one such trigger condition in one cycle of the signal. The software also features a specially designed algorithm which effectively eliminates the shaking of waveform display due to limited sampling rate compared with the signal frequency.

Trigger Mode

There are four trigger modes:

Auto

Frames of data are collected, analyzed and displayed continuously without searching for the trigger event inside the signal. Very fast display refresh rate can be achieved in this mode, however, the display may not be stable even if the signal under test is periodic, due to the fact that each frame of data may not be started at the same trigger position.

In this mode, selection for Trigger Source, Trigger Edge, Trigger Level and Trigger Delay is disabled and these parameters are not used.

Normal

Frames of data are collected, analyzed and displayed upon finding trigger events inside the signal. Very fast display refresh rate can be achieved in this mode if the software is triggered continuously by the signal. However, when the scan time (record length) is very short, the oscilloscope display may become unstable. It is recommended to use Slow Trigger Mode when the scan time (record length) is less than 500 µs for internal sound card, and 5 ms for external sound card. Note that these recommended values may vary with the sound card used.

Single

One frame of data are collected, analyzed and displayed upon the first trigger event inside the signal. The data acquisition process stops afterwards. This mode is ideal for transient signal recording.

Slow

Frames of data are collected, analyzed and displayed continuously upon finding trigger events inside the signal. The data acquisition will be reinitiated and restarted automatically every time a new frame of data is collected. The display refresh rate is thus slow in this mode. However it is recommended to use this mode when the scan time (record length) is very short and the display becomes unstable in Normal Trigger Mode.

Trigger Source

When only Channel A is sampled, the trigger source is fixed at Channel A and is not selectable.

When both Channel A and Channel B are sampled, the trigger source is selectable, either Channel A or Channel B.

Trigger Edge

Five types of Trigger Edge are available:

1. Up: When "Up" is selected, a trigger event is found when the signal is crossing the specified Trigger Level from below to above
2. Dn (Down): When "Dn" is selected, a trigger event is found when the signal is crossing the specified Trigger Level from above to below.
3. UD (Up or Down): When “UD” is selected, a trigger event is found when the signal is crossing the specified Trigger Level from below to above, or from above to below
4. JP (Jump): When “JP” is selected, a trigger event is found when the amount of change of the signal is greater than the amount specified by the Trigger Level. When the Trigger Level is positive, the change must be “Jump Up”. When the Trigger Level is negative, the change must be “Jump Down”. For example, under this mode, “Trigger Level=100%” means that the signal magnitude must increase by 100% of half of the ADC full-scale voltage (1/2 Vpp) between two adjacent sampled data points in order to be qualified for a trigger, and “Trigger Level = -100%” means that the signal magnitude must decrease by 100% of half of the ADC full-scale voltage (1/2 Vpp) between two adjacent sampled data points in order to be qualified for a trigger.
5. DF (Differential): When “DF” is selected, a trigger event is found when the absolute amount of change of the signal is greater than the absolute amount specified by the Trigger Level. Under this mode, Trigger Level can only be adjusted from 0~100%. For example, “Trigger Level=100%” means that the signal magnitude must increase or decrease by 100% of half of the ADC full-scale voltage (1/2 Vpp) between two adjacent sampled data points in order to be qualified for a trigger,

Trigger Level

Trigger Level is expressed as a percentage of half of the ADC full-scale voltage (1/2 Vpp). It is adjustable from -100% to 100%, except that when Trigger Edge is “DF”, Trigger Level can only be adjusted from 0~100%.

Trigger Delay

Trigger Delay spin box is located on the right hand side of the Trigger Level spin box. It is expressed as a percentage of the Record Length Per Scan and is adjustable from -100% to 100%.