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4.0 Calibration

The TR122 calibration compensates for variability in the analog instrument electronics.

The instrument is delivered fully calibrated and will not need any calibration efforts during

normal use. Calibrations are generally good for at least one year.

There are two aspects to the calibration of the TR122. The first is a familiar process

where the analog front end frequency compensation is adjusted to provide the best possible

representation of the incoming signal. This calibration step involves actual adjustment of

compensation capacitors in the front end electronics, similar to adjusting the compensation on

an oscilloscope probe. The other aspect involves compensation for gains and offsets of the

instrument electronics. This information will be discovered during calibration and stored in

a non-volatile memory in the TR122 as opposed to making any physical adjustments.

The primary objective of calibration is to be sure that transient record data displayed

or stored to disk matches the signal being measured within the limits of the instrument. For a

transient recorder, once the front end frequency compensation is adjusted the only other items

to compensate for are any irregularities in gain or offset present in the analog instrument

electronics. The gain calibration information stored in the instrument will be used to adjust

data retrieved from the instrument before it is presented on the screen or saved to disk. This is

an automatic function of the API library, so it will be present in any application which uses

this library.

In addition, the non-volatile memory is used to store information about the effect

of offset voltages on the instrument electronics and what offset is present initially. This

information is used to adjust the offset voltage applied such that zero offset is really zero offset

and any requested offset matches the intent. This information is applied every time the offset

is adjusted. The offset calibration tends to be different between settings of the instrument

attenuator electronics. Therefore, the API automatically reapplies the offset when the attenuator

settings are changed.

DDC TR122 User Manual

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