Calibration - TTI 1906 Service Manual

The instrument is software calibrated and retains its calibration constants in EEPROM. The
calibration procedure is programmed into the ROM and simply has to be stepped through by front
panel key presses or by remote interface commands.
The magnitude of the required calibration signal for each range and function is also programmed
into the ROM and is displayed as a calibration prompt at each step. The calibration point can
however be changed by remote command.
There is no facility for changing the calibration point from the front panel. Each meter function can
be calibrated separately, however certain calibration constants are calculated during the DC Volts
calibration procedure and used by other functions. It is therefore necessary to know that the DC
Volts function is calibrated before any other functions may be calibrated.
The calibration status of each function is recorded in a series of flags, one for each meter function
(see table below). The flags can be displayed when in calibrate mode (CAL‚ switch latched in,
CAL‚ LED on) by pressing the LOG‚ key. The flags are shown as a series of 1's and 0's across
the main display. All flags are set to 0 when a default calibration is performed and the appropriate
flag is set to 1 when true calibration constants are stored for each function.
Calibration Equipment
It is recommended that calibration equipment with accuracy five times that of the instrument is
used for DC Volts and Ohms and four times the specification for all other functions.
AC Voltage and current calibrations are performed at 500Hz. In addition frequency trimming of
the AC input attenuator is necessary at 200mV/20kHz, 2V/10kHz and 20V/50kHz.
Ohms calibration is performed in four-terminal mode, so the calibration equipment must provide a
remote sense facility.
Two low thermal EMF, zero Ohm links are necessary to short across the meter's input terminals
for certain calibration steps.
Default Calibration
For non-calibrated operation it is possible to load default calibration constants into the EEPROM
from the ROM. This is necessary when the instrument is switched on for the very first time and if
an error is detected in the EEPROM at power up.
To perform a default calibration the instrument must first be put into calibrate mode with the
instrument switched off. This is done by depressing the recessed CAL‚ switch located at the top
Fig. 7 - Calibration Flags

Calibration

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