National Instruments NI 6520 User manual

USER GUIDE

NI 6520/6521

This document describes how to use the National Instruments 6520 and

6521 data acquisition (DAQ) devices with NI-DAQ 7.5 or later. Device

specifications can be found on ni.com/manuals. If you have not already

installed the DAQ device, refer to the DAQ Getting Started Guide for

installation instructions.

The NI 6520/6521 contains five Form A single-pole single-throw (SPST)

non-latching relay outputs, three Form C single-pole double-throw (SPDT)

non-latching relay outputs, and eight channel-to-channel isolated industrial

inputs. The relay’s maximum switching power is 60 W/60 VA. The

maximum switching voltage for the NI 6520 is 30 Vrms/42.4 Vpk/

60 VDC. The maximum switching voltage for the NI 6521 is

150 VDC/VAC.

The NI 6520/6521 uses positive logic. A digital high energizes the relay,

and a digital low deenergizes it. In the energized state, the common (COM)

contact is connected to the normally open (NO) contact. For Form C relays

in the deenergized state, the common contact is connected to the normally

closed (NC) contact. For Form A relays in the deenergized state, the

common contact is not connected to the normally open (NO) contact. When

the board (PC) is powered off, the relays are deenergized.

Caution (NI 6521 Only) This 150 V Measurement Category II module features 1,400 Vrms

isolation between I/O channels and the backplane, as verified by a dielectric withstand test,

5 s maximum. For more information on hazardous voltage requirements and safety

information for the NI 6521, refer to the NI 6521 Isolation Voltages section.

Contents

Configuration .......................................................................................... 2

Functional Overview............................................................................... 3

Safety Information .................................................................................. 4

Related Documentation........................................................................... 6

Features ................................................................................................... 6

Digital Filtering................................................................................ 6

NI 6520/6521 User Guide 2 ni.com

Digital Filtering Example..........................................................7

Programmable Power-Up States.......................................................8

Change Detection .............................................................................9

Change Detection Example.......................................................9

Watchdog Timer...............................................................................10

Digital I/O................................................................................................10

I/O Connector ...................................................................................10

Pin Assignments ...............................................................................11

Signal Descriptions...........................................................................12

Optically Isolated Differential Inputs...............................................13

Sensing DC Voltages ................................................................13

Input Signal Connection Example.............................................14

Mechanical Relays............................................................................15

Relay Forms ..............................................................................15

Non-Latching Relays.................................................................15

Relay Power Ratings .................................................................15

Power-On and Power-Off Conditions .......................................16

Relay Signal Connection Example............................................16

Power Connections ..................................................................................17

Isolation Circuitry.............................................................................17

Input Isolation Circuitry ............................................................17

Output Isolation Circuitry .........................................................17

Isolation Voltages.............................................................................17

NI 6520 Isolation Voltages .......................................................17

NI 6521 Isolation Voltages .......................................................18

Protecting Inductive Loads...............................................................18

Cables and Accessories ...........................................................................20

NI 6520 Accessory Options..............................................................20

PCI-6521 Accessory Options ...........................................................21

PXI-6521 Accessory Options ...........................................................21

Specifications...........................................................................................22

Where to Go for Support .........................................................................22

Configuration

The NI 6520/6521 device is completely software configurable, so it is not

necessary to set jumpers for I/O configuration.

The PCI-6520/6521 is fully compliant with the PCI Local Bus

Specification, Revision 2.1, and the PXI-6521 devices are fully compliant

with the PXI Hardware Specification, Revision 2.1. The PCI/PXI system

automatically allocates all device resources, including the base address and

interrupt level. The NI 6520/6521 base address is mapped into PCI memory

space. It is not necessary to perform configuration steps after the system

powers up.

©National Instruments Corporation 3 NI 6520/6521 User Guide

The NI 6521 is designed to meet the requirements of UL/IEC 61010-1 and

is UL listed.

Refer to the driver software documentation for configuration instructions.

After the NI 6520/6521 device and the driver software are installed, the

DAQ device appears under the Devices and Interfaces branch of the MAX

configuration tree.

If the DAQ device does not appear in MAX, use the following

troubleshooting guidelines.

• Verify that you are using the correct version of NI-DAQ

(NI-DAQmx 7.5 or later). To download the most recent National

Instruments drivers, go to ni.com/drivers.

• Press <F5> to refresh the MAX window, or close and re-open MAX.

• Reboot the computer.

• Power off and unplug the computer or chassis, and install the device in

a different slot. Refer to the DAQ Getting Started Guide for installation

instructions and safety guidelines.

Functional Overview

Figure 1 illustrates the key functional components of the NI 6520/6521

device.

Figure 1. NI 6520/6521 Block Diagram

I/O Connector

PCI/PXI/CompactPCI Bus

Flash

Memory

PCI Bus

Interface

Photocouplers

Data/Control Data/Control

Configuration

Control

Relays

10 MHz

Clock

8 Digital

Inputs

8 Digital

Outputs

DIO Lines

Programmable

Power-Up States

Watchdog Timer

Change

Detection

Digital

Filtering

Industrial Digital

I/O Control FPGA

NI 6520/6521 User Guide 4 ni.com

Safety Information

The following section contains important safety information that you must

follow when installing and using National Instruments DIO devices.

Do not operate the device in a manner not specified in this document.

Misuse of the DIO device can result in a hazard. You can compromise the

safety protection built into the DIO device if it is damaged in any way. If

the DIO device is damaged, return it to National Instruments for repair.

Do not substitute parts or modify the DIO device except as described in this

document. Use the DIO device only with the chassis, modules, accessories,

and cables specified in the installation instructions. You must have all

covers and filler panels installed during operation of the DIO device.

Do not operate the DIO device in an explosive atmosphere or where there

may be flammable gases or fumes. If you must operate the DIO device in

such an environment, it must be in a suitably rated enclosure.

If you need to clean the DIO device, use a soft, nonmetallic brush. Make

sure that the DIO device is completely dry and free from contaminants

before returning it to service.

Operate the DIO device only at or below Pollution Degree 2. Pollution is

foreign matter in a solid, liquid, or gaseous state that can reduce dielectric

strength or surface resistivity. The following is a description of pollution

degrees:

• Pollution Degree 1 means no pollution or only dry, nonconductive

pollution occurs. The pollution has no influence.

• Pollution Degree 2 means that only nonconductive pollution occurs in

most cases. Occasionally, however, a temporary conductivity caused

by condensation must be expected.

• Pollution Degree 3 means that conductive pollution occurs, or dry,

nonconductive pollution occurs that becomes conductive due to

condensation.

You must insulate signal connections for the maximum voltage for which

the DIO device is rated. Do not exceed the maximum ratings for the DIO

device. Do not install wiring while the DIO device is live with electrical

signals. Do not remove or add connector blocks when power is connected

to the system. Avoid contact between your body and the connector block

signal when hot swapping modules. Remove power from signal lines

before connecting them to or disconnecting them from the DIO device.

©National Instruments Corporation 5 NI 6520/6521 User Guide

Operate the DIO device at or below the measurement category1marked

on the hardware label. Measurement circuits are subjected to working

voltages2and transient stresses (overvoltage) from the circuit to which they

are connected during measurement or test. Installation categories establish

standard impulse withstand voltage levels that commonly occur in

electrical distribution systems. The following is a description of installation

categories:

• Measurement Category I is for measurements performed on circuits

not directly connected to the electrical distribution system referred to

as MAINS3voltage. This category is for measurements of voltages

from specially protected secondary circuits. Such voltage

measurements include signal levels, special equipment, limited-energy

parts of equipment, circuits powered by regulated low-voltage sources,

and electronics.

• Measurement Category II is for measurements performed on circuits

directly connected to the electrical distribution system. This category

refers to local-level electrical distribution, such as that provided by a

standard wall outlet (for example, 115 V for U.S. or 230 V for Europe).

Examples of Measurement Category II are measurements performed

on household appliances, portable tools, and similar DIO devices.

• Measurement Category III is for measurements performed in the

building installation at the distribution level. This category refers to

measurements on hard-wired equipment such as equipment in fixed

installations, distribution boards, and circuit breakers. Other examples

are wiring, including cables, bus-bars, junction boxes, switches,

socket-outlets in the fixed installation, and stationary motors with

permanent connections to fixed installations.

• Measurement Category IV is for measurements performed at the

primary electrical supply installation (<1,000 V). Examples include

electricity meters and measurements on primary overcurrent

protection devices and on ripple control units.

1 Measurement categories, also referred to as installation categories, are defined in electrical safety standard IEC 61010-1.

2 Working voltage is the highest rms value of an AC or DC voltage that can occur across any particular insulation.

3 MAINS is defined as a hazardous live electrical supply system that powers equipment. Suitably rated measuring circuits may

be connected to the MAINS for measuring purposes.

NI 6520/6521 User Guide 6 ni.com

Related Documentation

The following documents contain information that you may find helpful as

you use this user guide:

•DAQ Getting Started Guide—This guide describes how to install the

NI-DAQ software, the DAQ device, and how to confirm that the device

is operating properly.

•NI-DAQmx Help—This help file contains information about using

NI-DAQmx to program National Instruments devices. NI-DAQmx

is the software you use to communicate with and control NI DAQ

devices.

•Measurement & Automation Explorer Help for NI-DAQmx—This

help file contains information about configuring and testing DAQ

devices using Measurement & Automation Explorer (MAX) for

NI-DAQmx, and information about special considerations for

operating systems.

•DAQ Assistant Help—This help file contains information about

creating and configuring channels, tasks, and scales using the DAQ

Assistant.

Note You can download these documents from ni.com/manuals.

Features

Digital Filtering

Use the digital filter option available on the NI 6520/6521 input lines to

eliminate glitches on input data. When used with change detection, filtering

can also reduce the number of changes to examine and process.

You can configure the digital input channels to pass through a digital filter

after the photocouplers, and you can control the timing interval the filter

uses. The filter blocks pulses that are shorter than half of the specified

timing interval and passes pulses that are longer than the specified interval.

Intermediate-length pulses—pulses longer than half of the interval but less

than the interval—may or may not pass the filter.

The filter operates on the inputs from the photocouplers. Photocouplers

turn on faster than they turn off and pass rising edges faster than falling

edges. As a result, the photocouplers can add up to 100 μs to a high pulse

or subtract up to 100 μs from a low pulse.

Note A 100 μs change is typical when IF= 16 mA, and RL= 10 kΩ.

©National Instruments Corporation 7 NI 6520/6521 User Guide

Table 1 lists the pulse widths guaranteed to be passed and blocked.

You can enable filtering on as many input lines as is necessary for your

application. All filtered lines share the same timing interval, which ranges

from 100 μs to 200 ms.

Internally, the filter uses two clocks: the sample clock and the filter clock.

The sample clock has a 100 ns period. The filter clock is generated by a

counter and has a period equal to one half of the specified timing interval.

The input signal is sampled on each rising edge of the sample clock, which

is every 100 ns. However, a change in the input signal is recognized only if

it maintains its new state for at least two consecutive rising edges of the

filter clock.

The filter clock is programmable and allows you to control how long a

pulse must last to be recognized. The sample clock provides a fast sample

rate to ensure that input pulses remain constant between filter clocks.

Digital Filtering Example

Figure 2 shows a filter configuration with an 800 ns filter interval (400 ns

filter clock).

Figure 2. Digital Filtering Example

Table 1. NI 6520/6521 Digital Filter Timing Intervals

Filter Interval

Pulse Width Passed Pulse Width Blocked

Low Pulse High Pulse Low Pulse High Pulse

tinterval tinterval + 100 μs tinterval – 100 μs(tinterval/2) + 100 μs(tinterval/2) – 100 μs

HHHHH

HLLHH

External

Signal

Filter

Clock

Sample Clock (100 ns)

External

Signal

Sampled

Filtered

Signal

NI 6520/6521 User Guide 8 ni.com

In periods A and B, the filter blocks the glitches because the external signal

does not remain steadily high from one rising edge of the filter clock to the

next. In period C, the filter passes the transition because the external signal

remains steadily high. Depending on when the transition occurs, the filter

may require up to two filter clocks—one full filter interval—to pass a

transition. Figure 2 shows a rising (0 to 1) transition. The same filtering

applies to falling (1 to 0) transitions.

Programmable Power-Up States

The default power-up state for Form C relays is deenergized (control bit is

low), which makes the contact connect at COM and NC. The Form C relay

status is user-configurable. If the power-up state of a Form C relay is

configured to energized (control bit is high), the contact connects at COM

and NO after power-up.

Figure 3. Programmable Power-Up States for Form C Relays

The default power-up state for Form A relays is deenergized (control bit is

low), which makes the contact open at COM and NO. The Form A relay

status is user-configurable. If the power-up state of a Form A relay is

configured to energized (control bit is high), the contact connects at COM

and NO after power-up.

Figure 4. Programmable Power-Up States for Form A Relays

User-configurable power-up states are useful for ensuring that the

NI 6520/6521 power up in a known state.

To use MAX (recommended) to program the power-up states, select

the device and click the Properties button. Refer to the software

documentation for information about how to program the power-up states

using NI-DAQ with LabVIEW or other National Instruments application

development environments (ADEs).

Note The response time of programmable power-up states is 400 ms.

COM NC

COM

Control Bit Is High (1)

Control Bit Is Low (0)

NOCOM NOCOM

Control Bit Is High (1)

Control Bit Is Low (0)

©National Instruments Corporation 9 NI 6520/6521 User Guide

Change Detection

You can program the NI 6520/6521 device to send an interrupt when a

change occurs on any input line.

The DIO device can monitor changes on selected input lines or on all input

lines. It can monitor for rising edges (0 to 1), falling edges (1 to 0), or both.

When an input change occurs, the DIO device generates an interrupt, and

the NI-DAQ driver then notifies the software.

Note Excessive change detections can affect system performance. Use digital filtering to

minimize the effects of noisy input lines.

The DIO device sends a change detection when any one of the changes

occurs, but it does not report which line changed or if the line was rising or

falling. After a change, you can read the input lines to determine the current

line states. The maximum rate of change detection is determined by the

software response time, which varies from system to system.

An overflow bit indicates that an additional rising or falling edge has been

detected before the software could process the previous change.

Refer to the software documentation for information about how to set up

and implement the change detection.

Change Detection Example

Table 2 shows a change detection example for six bits of one port.

This example assumes the following line connections:

• Bits 7, 6, 5, and 4 are connected to data lines from a four-bit TTL

output device. The DIO device detects any change in the input data

so you can read the new data value.

• Bit 1 is connected to a limit sensor. The DIO device detects rising

edges on the sensor, which correspond to over-limit conditions.

Table 2. Change Detection Example

Bit

7 6 5 4 3 2 1 0

Changes to detect — —

Enable rising-edge detection yes yes yes yes no no yes no

Enable falling-edge detection yes yes yes yes no no no yes

NI 6520/6521 User Guide 10 ni.com

• Bit 0 is connected to a switch. The software can react to any switch

closure, which is represented by a falling edge. If the switch closure is

noisy, enable digital filtering for this line.

In this example, the DIO device reports rising edges only on bit 1, falling

edges only on bit 0, and rising and falling edges on bits 7, 6, 5, and 4. The

DIO device reports no changes for bits 3 and 2. After receiving notification

of a change, you can read the port to determine the current values of all

eight lines. You cannot read the state of any lines that are configured for

change detection until the change detection interrupt occurs.

Watchdog Timer

The watchdog timer is a software configurable feature used to set critical

outputs to safe states in the event of a software failure, a system crash, or

any other loss of communication between the application and the

NI 6520/6521 while power is provided to the PC/board.

When the watchdog timer is enabled, if the NI 6520/6521 does not receive

a watchdog reset software command within the time specified for the

watchdog timer, the outputs go to a user-defined safe state and remain in

that state until the watchdog timer is disarmed by the application and new

values are written, the NI 6520/6521 is reset, or the computer is restarted.

The expiration signal that indicates an expired watchdog will continue to

assert until the watchdog is disarmed. After the watchdog timer expires, the

NI 6520/6521 ignores any writes until the watchdog timer is disarmed.

You can set the watchdog timer timeout period to specify the amount of

time that must elapse before the watchdog timer expires. The counter on the

watchdog timer is configurable up to (232 – 1) ×100 ns (approximately

seven minutes) before it expires.

Digital I/O

I/O Connector

The 37-pin D-SUB connector on the NI 6520/6521 provides access to eight

isolated digital inputs and 8 relay outputs. For easy connection to the digital

I/O connector, use the National Instruments 37-pin D-SUB accessories. For

a list of compatible 37-pin accessories, refer to the Cables and Accessories

section.

Caution Do not make connections to the digital I/O that exceed the maximum I/O

specifications. Doing so may permanently damage the NI 6520/6521 and the chassis. Refer

to the Signal Descriptions section and the device specifications for information about

maximum input ratings.

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