VXi VT1422A 사용자 설명서

The Calibration subsystem provides for two major categories of calibration.

1. "A/D Calibration"— In these procedures, an external multimeter is used to 

calibrate the A/D gain on all five of its ranges. The multimeter also determines 
the value of the VT1422A's internal calibration resistor. The values generated 
from this calibration are then stored in nonvolatile memory and become the 
basis for "Working Calibrations. These procedures each require a sequence of 
several commands from the CALibration subsystem (CAL:CONFIG

…, 

… and CAL:STORE ADC). Always execute *CAL? or a 

CAL:TARE operation after A/D Calibration.

2. "Working Calibration"—Which has three levels (see Figure 7-3):

-- "A/D Zero"—This function quickly compensates for any short term A/D 

converter offset drift. This would be called the auto-zero function in a 
conventional voltmeter. In the VT1422A where channel scanning speed is of 
primary importance, this function is performed only when the 
CAL:ZERO? command is executed. Execute CAL:ZERO? as often as the 
control setup will allow.

-- "Channel Calibration"—This function corrects for offset and gain errors 

for each module channel. The internal current sources are also calibrated. 
This calibration function corrects for thermal offsets and component drift 
for each channel out to the input side of the Signal Conditioning Plug-On 
(SCP). All calibration sources are on-board and this function is invoked 
using either the *CAL? or CAL:SETup command.

-- "Channel tare"—This function (CAL:TARE) corrects for voltage offsets in 

external system wiring. Here, the user places a short across transducer 
wiring and the voltage that the module measures is now considered the 
new "zero" value for that channel. The new offset value can be stored in 
non-volatile calibration memory (CAL:STORE TARE) but is in effect 
whether stored or not. System offset constants which are considered 
long-term should be stored. Offset constants which are measured relatively 
often would not require non-volatile storage. CAL:TARE automatically 
executes a *CAL?

-- "Remote Channel Calibration"—This function corrects for gain and offset 

errors in each channel of a Remote Signal Conditioning unit (RSC). 
Each RSC has its own calibration voltage source as well as shorting 
switches. The calibration source is measured through dedicated analog 
connections between the VT1539A SCP and the RSC. The source is then 
used to stimulate the RSCs amplifiers to calibrate gain. The shorting 
switches provide a zero volt source to calibrate offset.