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2.2 Oscilloscope Mode

Keep in mind that a transient recorder is not an oscilloscope. Although the TR122

software makes a valiant effort at imitating an oscilloscope, the user is bound to be disappointed

in comparison to instruments designed for this purpose. A transient recorder is somewhat like a

deep memory oscilloscope restricted to operate in the single shot trigger mode. The TR122

oscilloscope mode uses an independent software thread to record and display transient records

of the entire two million sample memory at a rate dependant on the selected horizontal time base.

To achieve slower timebases the software must lower the sample rate and compress the data. At

faster horizontal settings this is fairly undetectable, while at slower settings the transient recorder

characteristics can be seen as full memory records are collected and displayed. On the other

hand, significant time frames of data are always available, making it easier to capture activity

well before or after the trigger.

The oscilloscope mode is intended to be used to establish the settings required to perform

a transient measurement. Vertical and horizontal selections along with trigger source selections

have an immediate effect on how the data is being acquired and displayed. The user is likely

familiar with most of the controls and settings provided. The typical vertical, horizontal, and

trigger menus of an oscilloscope are accessed by clicking the tabs at the upper left of the

window. The following discussion provides some additional insight into how these controls

are used.

2.2.1 Vertical Settings

The vertical controls for each channel are under the tabs marked CH1 and CH2 as shown

in Figure 2.1 above. The oscilloscope screen in any mode always displays only 8-bits of the

12-bit data stream provided by the TR122. The Volts/Div 8-Bit setting assumes that the software

will be concerned with only the upper 8 bits. Of course, when data are eventually saved to disk

in transient mode, all 12 bits will always be represented.

To allow the user to examine what is happening within the lower bits, the software

provides a setting called Bit Mag. This can magnify the image to 1,2,4,8,or16 by sliding the

visible bits down the sample by 0 to 4 bits. It should be noted that the offset and trigger settings

are calibrated to be valid with the 8-bit display and will not be coherent with the Bit Mag set to

greater than 1. The volts per division display below the oscilloscope screen will always display a

value taking the Bit Mag into account. The volt per division display at either location can be

used to adjust the front end attenuator of the TR122.

All controls in the TR122 software can be adjusted by clicking on them with the mouse

buttons. For most, though not all, controls the left mouse button will increase the value

of the control and the right mouse button will return its value.

The coupling, input impendence, and probe settings are as they would be on an

oscilloscope. The probe setting has no physical effect on the instrument, but simply multiplies

the displayed values for volts per division for ease of use when an oscilloscope probe is

connected to the instrument.

DDC TR122 User Manual

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