User's Manual

Chapter 2 Hardware Overview

Internally Calibrating the NI 5911

Internally calibrate your NI 5911 with a software function or a

LabVIEW VI. Read more about the function,

niScope_CalSelfCalibrate

, in your NI-SCOPE Function Reference

Help file. LabVIEW users, see the context sensitive help (Help»Show

Context Help

)

for

niscope Cal Self Calibrate. vi

When Internal Calibration Is Needed

To provide the maximum accuracy independent of temperature changes,

the NI 5911 contains a heater that stabilizes the temperature of the most

sensitive circuitries on the board. However, the heater can accommodate

for temperature changes over a fixed range of ±5 °C. When temperatures

exceed this range, the heater no longer is able to stabilize the temperature,

and signal data becomes inaccurate. When the temperature range has been

exceeded, you receive a warning, and you need to perform an internal

calibration.

What Internal Calibration Does

Internal calibration performs the following operations:

1. The heater is set to regulate over a range of temperatures centered at

the current environmental temperature. The circuit components require

a certain amount of time to stabilize at the new temperature. This

temperature stabilization accounts for the majority of the calibration

time.

2. Gain and offset are calibrated for each individual input range.

3. The linearity of the ADC is calibrated using an internal sinewave

generator as reference.

4. The time-to-digital converter used for RIS measurements is calibrated.

Note

Do not apply high-amplitude or high-frequency signals to the NI 5911 during

internal calibration. For optimal calibration performance, disconnect the input signal from

the NI 5911.

Why Errors Occur During Acquisition

The NI 5911 has circuitry to detect error conditions that may affect the

acquired data. The NI 5911 uses a heater circuit to maintain constant

temperature on the critical circuitry used in flexible resolution mode. If this

circuit is unable to maintain the temperature within specification, an error

is generated. This error indicates that the temperature of the ADC is out