Introduction; Calibration; Methods Of Calibration; Preparing For Calibration - Fluke 2680A Service Manual

Introduction

This section of the Service Manual provides a complete set of manual calibration
procedures for the 2680A/2686A. The calibration procedures are performed periodically
as well as after service or repair. There are no calibration procedures for the
2680A/2686A chassis nor for the DIO module. Only verification tests are run on those
items. The calibration is only performed on the analog A/D modules such as the precision
A/D input module (PAI) and the fast A/D input module (FAI).

Calibration

The 2680A/2686A device features module calibration that is performed over the RS-232
interface using ASCII characters. It is not necessary to open the module case. Each
analog A/D module must be calibrated separately. Using known reference sources,
closed-case calibration has many advantages. There are no parts to disassemble, no
mechanical adjustments to make, and the module can be calibrated by an automated
calibration system. The modules should normally be calibrated on a regular cycle,
typically every 90 days to 1 year. The chosen calibration cycle depends on the accuracy
specification you wish to maintain. The module should also be calibrated if it fails the
performance test or has undergone repair.
The calibration mode requires initialization through a built-in calibration command. To
enter the calibration mode, use the command CAL_MODE SPLUNGE. When calibration
is enabled, the secondary display shows 'CAL'. To disable the calibration mode, enter
CAL_MODE OFF. If you have entered calibration and wish to exit, send CAL_MODE
OFF, or just turn the device power off. You cannot stop calibration by entering front
panel commands.
Once the device is in calibration mode, closed-case calibration is made for the four
calibration groups as follows:
Volts DC
Volts AC
Resistance
Frequency
Once begun, each group must be completed successfully for the results of the calibration
to be made permanent. It is not necessary to perform all calibration groups.

Methods of Calibration

Calibration takes place using a host computer in a terminal mode. With this method
all commands and responses are considered individually.
Calibration uses the device RS-232 serial interface. It is possible to develop an
automatic calibration routine using the RS-232 commands. Procedures cannot be
performed over the network interface or from the device front panel.

Preparing for Calibration

Complete the following procedure to prepare for calibration.
1. Connect the device RS-232 serial port to a host computer COM serial port as shown
in Figure 5-1. The "RS" cables used are standard null-modem cables (reversed
transmit and receive lines) that may be ordered from Fluke.

Calibration

5

Introduction

5-3