Offsets and Calibration

All internal analog channel offsets in BitScope are factory calibrated.

This means that when the inputs are ground referenced (i.e. connected to ground) and the offset control is reset, the trace will appear in the center of display (i.e. at exactly zero volts).

However, there are circumstances where you may wish to make changes to this offset calibration; temporarily to eliminate offsets appearing in the signal under specific circumstances and permanently to recalibrate the channel if temperature or time make it necessary.

Offset Assignment

Sometimes a DC offset may appear in a signal which you want to ignore.

[10] Input Offset Assignment

Alternatively you may find that for precise measurement you wish to finesse the calibration of a given range or prescale.

Offset calibration is available via the menu shown in Fig [10] that appears upon right-clicking the zero offset button (12).

For a given source, range, prescale and the input referenced, offset controls can relocate the trace to the center of the display.

With the trace centered, selecting Assign Input Offset recalibrates the channel offset for that channel setup.

That is, it assigns a temporary calibration offset to the channel which ensures that the reference signal appears exactly at the center of the display.

All subsequent measurements will be made referenced to the assigned offset, not zero volts.

Offset Calibration

If offsets appear on a channel on a particular source, range or prescale when the input is properly ground referenced, the internal channel offsets may require persistent recalibration.

[11] Set Ground Reference

This is achieved the same way as offset assignment described above but there is a specific procedure that must then be followed to calibrate all the channel offsets correctly.

It is important to understand that an internal offset can appear in each possible signal path through the analog channel circuitry.

That is, a different calibration parameter may be required for each source, range and prescale value. In some BitScopes this adds up to quite a few parameters (for example there are 20 possible parameters for each channel in BS310).

In practice the number of different parameters is much smaller (5 per channel in BS310) so in relatively few steps it is possible to recalibrate all channel offsets.

The first step in all cases is assignment of the channel's global ground reference.

[12] Save Calibration Settings

When a specific channel source, range and prescale is selected, the channel's global ground reference may be assigned as shown in Fig [11].

Next a small set of input offsets for other source, range and prescale values are assigned. At this point they may be saved to the BitScope as shown in Fig [12].

When this is done, all the channel calibration parameters are recalculated based on the assigned input offsets and saved to flash memory to be reused automatically in future.

The set of channel settings for which the input offset must be (re)assigned to enable this complete recalibration of the channel depends on the BitScope model concerned.

Offset Calibration Procedures

The tables below enumerate the offset calibration steps per channel for each BitScope model.

All inputs must be ground referenced and channels normalized before attempting calibration.

All channels must select POD OFF except where noted in the tables below.

BitScope Model 325 Channel Offset Calibration Procedure

BitScope Model 120 Channel Offset Calibration Procedure

BitScope Model 100 Channel Offset Calibration Procedure

BitScope Model 442 Channel Offset Calibration Procedure

BitScope Model 310 Channel Offset Calibration Procedure

Note: it is recommended that both channels be calibrated simultaneously for this model.

BitScope Model 440 Channel Offset Calibration Procedure

BitScope Model 300 Channel Offset Calibration Procedure

Note: it is recommended that both channels be calibrated simultaneously for this model.

BitScope Model 50 Channel Offset Calibration Procedure

Note: only channel A needs to be calibrated.

BitScope Model 220 Channel Offset Calibration Procedure

Note: it is recommended that both channels be calibrated simultaneously for this model.