National Instruments NI cDAQ-9178 User Manual

5-14 | ni.com
Chapter 5 Counters
With sample clocked frequency measurements, ensure that the frequency to measure is twice as
fast as the sample clock to prevent a measurement overflow.
Choosing a Method for Measuring Frequency
The best method to measure frequency depends on several factors including the expected
frequency of the signal to measure, the desired accuracy, how many counters are available, and
how long the measurement can take. For all frequency measurement methods, assume the
following:
fx is the frequency to be measured if no error
fk is the known source or gate frequency
measurement time (T) is the time it takes to measure a single sample
Divide down (N) is the integer to divide down measured frequency, only used in
large range two counters
fs is the sample clock rate, only used in sample clocked frequency
measurements
Here is how these variables apply to each method, summarized in Table 5-2.
• One counter—With one counter measurements, a known timebase is used for the source
frequency (fk). The measurement time is the period of the frequency to be measured, or 1/fx.
• Two counter high frequency—With the two counter high frequency method, the
second counter provides a known measurement time. The gate frequency equals
1/measurement time.
• Two counter large range—The two counter larger range measurement is the same as a
one counter measurement, but now the user has an integer divide down of the signal. An
internal timebase is still used for the source frequency (fk), but the divide down means that
the measurement time is the period of the divided down signal, or N/fx where N is the divide
down.
• Sample clocked—For sample clocked frequency measurements, a known timebase is
counted for the source frequency (fk). The measurement time is the period of the sample
clock (fs).
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National Instruments NI cDAQ-9178 Specifications

General

Chassis Type	CompactDAQ
Number of Slots	8
USB Interface	USB 2.0
Dimensions	25.7 cm x 9.4 cm x 9.4 cm (10.1 in. x 3.7 in. x 3.7 in.)
Host Interface	USB
Power Supply	100-240 VAC
Operating Temperature	0 to 55 °C
Storage Temperature	-40 to 70 °C
Supported modules	C Series I/O modules
Storage temperature range	-40 to 70 °C
Power requirements	100-240 VAC
Maximum Sample Rate	1 MS/s per channel
Maximum sampling rate	1 MS/s per channel

Summary

Getting Started with the cDAQ Chassis

Safety Guidelines

Essential safety precautions, including hazardous voltages and EMC.

Hardware Symbol Definitions

Explanation of symbols marked on the cDAQ chassis.

Unpacking

Procedures for safely unpacking and handling the cDAQ chassis to prevent ESD.

Installing the cDAQ Chassis

Step-by-step guide for installing the cDAQ chassis and software.

Using the cDAQ Chassis on a Desktop

How to use the chassis on a desktop, including mounting kits.

Mounting the cDAQ Chassis on a Panel

Methods for panel mounting the cDAQ chassis.

Mounting the cDAQ-9174/9178 on a DIN Rail

Instructions for mounting the cDAQ chassis on a DIN rail.

cDAQ Chassis Features

Overview of chassis components like LEDs, USB port, BNC connectors, and grounding screw.

Removing Modules from the Chassis

Instructions for safely removing C Series modules from the chassis.

Using the cDAQ Chassis

Explains chassis interface, STC3, and parallel vs. serial DIO modules.

Analog Input

Analog Input Triggering Signals

How to initiate analog input tasks using triggers (Start, Reference, Pause).

Analog Input Timing Signals

Signals controlling the timing of analog input acquisition.

AI Sample Clock Signal

Controls the timing of AI data sampling from channels.

AI Convert Clock Signal Behavior

How AI convert clocks function for different analog input modules.

AI Module Types

Behavior of Scanned, SSH, Sigma-Delta, and Slow Sample Rate modules.

Analog Output

Analog Output Data Generation Methods

Methods for generating analog output signals (software vs. hardware timed).

Buffered Analog Output

Using onboard FIFO for storing and outputting analog data.

Analog Output Triggering Signals

How to initiate analog output tasks using triggers (Start, Pause).

Analog Output Timing Signals

Signals controlling the timing of analog output generation.

AO Sample Clock Signal

Controls the timing of AO data updates to channels.

Minimizing Output Glitches

Techniques to reduce glitches in analog output signals.

Digital Input/Output and PFI

Digital Input/Output Overview

Basic digital I/O functionality and types of DIO modules.

Digital Input Signals

Triggering, timing, and filtering for digital input operations.

Digital Output Signals

Data generation, triggering, and timing for digital output operations.

PFI and PFI Filters

Using Programmable Function Interface terminals and their filters.

Counters

Counter Input Applications

How counters measure edges, pulses, frequency, period, and position.

Counter Output Applications

How counters generate pulses, pulse trains, and frequencies.

Counter Timing Signals

Signals controlling counter operations like source, gate, and arming.

Other Counter Features

Cascading counters, prescaling, and synchronization modes.

Digital Routing and Clock Generation

Digital Routing

Manages data flow between bus interface and subsystems.

Clock Routing

Circuitry for generating and routing clock signals.

Timebases

Overview of available clock sources like 80 MHz, 20 MHz, and 100 kHz.

Where to Go from Here

Example Programs

Locating and using example programs for NI-DAQmx.

Documentation and Resources

Links to manuals for cDAQ chassis, C Series modules, and NI software.

Training and Support

Information on NI training courses and technical support channels.

NI Services

Services and Resources

Overview of NI's support services including maintenance, warranty, and calibration.

Training and Certification

Programs to enhance application development proficiency and productivity.

Technical Support

Accessing software drivers, KnowledgeBase, and forums for help.

Declaration of Conformity (DoC)

NI's claim of compliance with European directives for EMC and safety.