National Instruments NI 9478 User manual

OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9478
16-Channel, 0–50 V, Sinking Digital Output Module
with Programmable Current Limits
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NI 9478 Operating Instructions and Specifications 2 ni.com
This document describes how to use the National Instruments 9478
and includes specifications and pin assignments for the NI 9478.
Visit ni.com/info and enter rdsoftwareversion to determine
which software youneed for the modules youare using. For
information about installing, configuring, and programming the
system, refer to the system documentation. Visit ni.com/info
and enter cseriesdoc for information about C Series
documentation.
Note The safety guidelines and specifications in this
document are specific to the NI 9478. The other
components in the system might not meet the same safety
ratings and specifications. Refer to the documentation for
each component in the system to determine the safety
ratings and specifications for the entire system. Visit
ni.com/info and enter cseriesdoc for information
about C Series documentation.

© National Instruments Corp. 3 NI 9478 Operating Instructions and Specifications
Safety Guidelines
Operate the NI 9478 only as described in these operating
instructions.
Hot Surface This icon denotes that the component may be
hot. Touching this component may result in bodily injury.
Safety Guidelines for Hazardous Locations
The NI 9478 is suitable for use in Class I, Division 2, Groups A, B,
C, D, T4 hazardous locations; Class I, Zone 2, AEx nA IIC T4, and
Ex nA IIC T4 hazardous locations; and nonhazardous locations
only. Follow these guidelines if youare installing the NI 9478 in a
potentially explosive environment. Not following these guidelines
may result in serious injury or death.
Caution Do not disconnect I/O-side wires or connectors
unless power has been switched off or the area is known
to be nonhazardous.
Caution Do not remove modules unless power has been
switched off or the area is known to be nonhazardous.

NI 9478 Operating Instructions and Specifications 4 ni.com
Caution Substitution of components may impair
suitability for Class I, Division 2.
Caution For Zone 2 applications, install the system
in an enclosure rated to at least IP 54 as defined by
IEC 60529 and EN 60529.
Caution For Zone 2 applications, install a protection
device across the external power supply and the COM
pin. The device must prevent the external power supply
voltage from exceeding 70 V if there is a transient
overvoltage condition.
Special Conditions for Hazardous Locations Use in Europe
This equipment has been evaluated as Ex nA IIC T4 equipment
under DEMKO Certificate No. 07 ATEX 0626664X. Each module
is marked II 3G and is suitable for use in Zone 2 hazardous
locations. If youare using the NI 9478 in Gas Group IIC hazardous
locations or in ambient temperatures of –40 °C ≤Ta ≤70 °C, you
must use the device in an NI chassis that has been evaluated as
EEx nC IIC T4, Ex nA IIC T4, or Ex nL IIC T4 equipment.

© National Instruments Corp. 5 NI 9478 Operating Instructions and Specifications
Special Conditions for Marine Applications
Some modules are Lloyd’s Register (LR) Type Approved for
marine applications. To verify Lloyd’s Register certification,
visit ni.com/certification and search for the LR certificate,
or look for the Lloyd’s Register mark on the module.
Caution To meet radio frequency emission requirements
for marine applications, use shielded cables and install
the system in a metal enclosure. Suppression ferrites
must be installed on power supply inputs near power
entries to modules and controllers. Power supply and
module cables must be separated on opposite sides of
the enclosure and must enter and exit through opposing
enclosure walls.

NI 9478 Operating Instructions and Specifications 6 ni.com
Connecting the NI 9478
The NI 9478 has a 37-pin DSUB connector that provides
connections for the 16 digital output channels.
Figure 1. NI 9478 Pin Assignments
DO0
DO1
DO2
DO3
DO4
DO5
DO6
DO7
Vsup
Vsup
DO8
DO9
DO10
DO11
DO12
DO13
DO14
DO15
NC
COM
COM
COM
COM
COM
COM
COM
COM
Vsup
Vsup
COM
COM
COM
COM
COM
COM
COM
COM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37

© National Instruments Corp. 7 NI 9478 Operating Instructions and Specifications
Each channel of the NI 9478 has a DO pin to which youcan
connect the load youwant to control. Each channel also has a COM
pin. National Instruments recommends youprovide independent
COM wiring for each channel to minimize current flow in the
COM wiring. The COM pins are all connected together internally.
Yo umust connect an external power supply to the NI 9478. This
power supply provides the current for the devices youconnect to
the module. Connect the positive lead of the power supply to Vsup
and the negative lead of the power supply to COM.
Caution Do not remove or insert modules if the external
power supply connected to the Vsuppin is powered on.
The NI 9478 has current sinking outputs, meaning the DO pin is
driven to COM when the channel is turned on.
Yo ucan directly connect the NI 9478 to a variety of industrial
devices such as solenoids, motors, actuators, relays, and lamps.
Make sure the devices youconnect to the NI 9478 are compatible
with the output specifications of the module. Refer to the
Specifications section for more information about the output
specifications.

NI 9478 Operating Instructions and Specifications 8 ni.com
Connect the device to DO and the positive lead of the power
supply. Refer to Figure 2 for an illustration of how to connect
a device to the NI 9478.
Figure 2. Connecting a Device to the NI 9478
Yo umust connect the Vsuppin to the power supply to enable a
weak cable clamping diode that protects the module from cable
inductance flyback. This flyback voltage results from small
amounts of energy stored in the inductance of the cabling. Refer
to the Using Long Cables section for more information about
protection from cable inductance flyback. Youstill must install an
external flyback diode when switching inductive loads. Refer to the
Protecting the Module from Flyback Voltages section for more
information about installing a flyback diode.
Device +
–
NI 9478
COM
Vsup
DO
External
Power
Supply
Cable
Clamp

© National Instruments Corp. 9 NI 9478 Operating Instructions and Specifications
Protecting the Module from Flyback Voltages
If the module is switching an inductive or energy-storing device
such as a solenoid, motor, or relay, and the device does not have
flyback protection, install an external flyback diode as shown in
Figure 3. Refer to the Using Long Cables section for more
information about protection from cable inductance flyback.
Figure 3. Connecting a Flyback Diode to the NI 9478
+
–
NI 9478
COM
DO External
Power
Supply
Vsup
Cable
Clamp Device

NI 9478 Operating Instructions and Specifications 10 ni.com
Using Long Cables
The inductance of the cabling that connects the NI 9478, the loads,
and the external supply stores up energy when a channel is on and
passing current through the cables. Each time a channel is turned
off, the energy stored in the cables is released as flyback voltage
and dissipates as heat in the NI 9478. The total power dissipated in
the module increases with higher switching frequencies, higher
currents, and longer cable lengths. The cable length is the total
distance from the digital output pin of the NI 9478 channel,
through the load, through the external power supply, and back
to the COM pin, as shown in Figure 4.
Figure 4. Cable Length of the NI 9478
NI 9478COM
Vsup
DO
+
–
External
Power
Supply
Cable
Length
Load
Cable
Clamp

© National Instruments Corp. 11 NI 9478 Operating Instructions and Specifications
Yo ucan reduce the effective length of the cable by adding a
capacitor close to the NI 9478 across the power supply leads and
adding a diode from the digital output line to the Vsuppin line.
National Instruments recommends that youuse a capacitor with a
capacitance of at least 20 μF. In this case, the effective length of the
cable is the distance from the output pin, through the new diode,
through the capacitor, and back to the COM pin, as shown in
Figure 5.
Figure 5. Cable Length of the NI 9478 with a Capacitor and Diode
NI 9478COM
Vsup
DO
+
–
External
Power
Supply
Cable
Length
Load
Cable
Clamp

NI 9478 Operating Instructions and Specifications 12 ni.com
I/O Protection
The NI 9478 provides protection against overcurrent and
short-circuit conditions.
Output Current Limit Thresholds
The NI 9478 provides two configurable current limit thresholds
for the module, Limit A and Limit B. The NI 9478 continuously
monitors the current through each output channel and detects if
the current exceeds either of the current limit thresholds. Youcan
configure the current limit thresholds and check the current limit
output status in software to determine if the current through each
channel has exceeded the current limit thresholds. Refer to the
software help for more information about configuring current
limits and checking output status. Visit ni.com/info and enter
cseriesdoc for information about C Series documentation.
Overcurrent Protection
Yo ucan configure each channel on the NI 9478 to disable the
output if the current through the output exceeds either current
limit threshold. This protects the NI 9478 from overcurrent and
short-circuit conditions and provides a way to limit the current
through an external device.

© National Instruments Corp. 13 NI 9478 Operating Instructions and Specifications
Some applications require a large inrush current when a channel is
first turned on. If this inrush current exceeds the maximum current
limit threshold, youmay need to disable overcurrent protection by
programming the channel to have no current limit. Refer to the
software help for more information about configuring current
limits. Visit ni.com/info and enter cseriesdoc for information
about C Series documentation.
Caution The NI 9478 is not protected against output
overcurrent or short-circuit conditions when overcurrent
protection is disabled. If youdisable overcurrent
protection, ensure that the wiring is correct and that you
are operating the NI 9478 within the specifications.
The total amount of current that youcan switch with a channel
depends on the duty cycle of the channel, the ambient temperature,
the switching frequency, and the amount of current switched by
other channels within the same module at the same time. Refer to
the Safe Operating Current section for more information about the
current specifications.

NI 9478 Operating Instructions and Specifications 14 ni.com
Overcurrent Refresh
The NI 9478 provides an overcurrent refresh setting that enables
a channel to automatically recover within the specified overcurrent
refresh period if the channel exceeds its current limit threshold.
If overcurrent refresh is disabled, the channel remains off after an
overcurrent condition until software sends a command to turn the
channel back on. Refer to the software help for more information
about overcurrent refresh. Visit ni.com/info and enter
cseriesdoc for information about C Series documentation.
Safe Operating Current
The maximum allowable output current depends on the output
frequency and cable lengths. Higher output currents, higher output
frequencies, and longer cable lengths can contribute to power
dissipating and heat increasing in the NI 9478. The Specifications
section gives allowable current and frequency specifications if you
use 2 meters of cabling. For other operating conditions, youcan
find the safe operating specifications for the NI 9478 by calculating
the percentage of the total allowable power each output channel
dissipates given the output current, frequency, and cable length

© National Instruments Corp. 15 NI 9478 Operating Instructions and Specifications
for that channel. Use the following equation to calculate the
percentage of the total power budget each output channel uses in
your application.
To verify that your application keeps the NI 9478 within safe
operating specifications, calculate the average percentage of
total allowable power each channel uses, then add together the
percentages for all the channels. For operation in ambient
temperatures from 55 to 70 °C, the total average power of all
channels must remain under 100%. For temperatures below 55 °C,
the total average power of all channels can run up to 150%.
where Pis the percentage of total allowable power the channel uses
Iout is the output current in amperes while the channel is on
length is the total cable length in meters, shown in Figure 4
freq is the frequency rate in kHz at which the output channel goes
through an on-off cycle
P4% Iout
2
⎝⎠
⎛⎞
0.12% length 0.2–()Iout
2
⎝⎠
⎛⎞
0.04% Iout 1+()+freq+=

NI 9478 Operating Instructions and Specifications 16 ni.com
Example One
Yo uare driving a load with 2.0 meters of cable through a cycle in
which the NI 9478 is on and passing 1.25 A of current for 40 μs,
then off for 10 μs. The output period is 50 μs (40 μs + 10 μs) so the
output frequency is 20 kHz. The channel uses 14.8% of the total
power budget, as shown in the following equation.
4% 1.252 ()0.12% 2.0 0.2–()1.252 ()0.04% 1.25 1+()+[]20+14.8%=

© National Instruments Corp. 17 NI 9478 Operating Instructions and Specifications
Example Two
Yo uare driving a load with 2.0 meters of cable through a cycle in
which the NI 9478 first is constantly on and passing 3 A of current
for 0.25 seconds, then drives the load at 20 kHz with 1.25 A current
for 1.25 seconds, then drives the load off for 4 seconds. While the
NI 9478 is constantly on, the output frequency is 0 kHz and the
channel uses 36% (4% × 32) of the total power budget. Example
One shows that while the NI 9478 is driving at 20 kHz, the channel
uses 14.8% of the total power budget. While the NI 9478 is off, the
channel uses 0% of the power budget. The average percentage of
total allowable power over the complete 5.5 second cycle is 5%,
as shown in the following equation.
36% 0.25s()14.8 % 1.25 s()0% 4s()++
5.5s
------------------------------------------------------------------------------------------------- 5%=

NI 9478 Operating Instructions and Specifications 18 ni.com
Sleep Mode
This module supports a low-power sleep mode. Support for sleep
mode at the system level depends on the chassis that the module is
plugged into. Refer to the chassis manual for information about
support for sleep mode. If the chassis supports sleep mode, refer to
the software help for information about enabling sleep mode. Visit
ni.com/info and enter cseriesdoc for information about
C Series documentation.
Typically, when a system is in sleep mode, youcannot
communicate with the modules. In sleep mode, the system
consumes minimal power and may dissipate less heat than it
does in normal mode. Refer to the Specifications section for more
information about power consumption and thermal dissipation.

© National Instruments Corp. 19 NI 9478 Operating Instructions and Specifications
Specifications
The following specifications are typical for the range –40 to 70 °C
unless otherwise noted. All voltages are relative to COM unless
otherwise noted.
Output Characteristics
Number of channels.......................... 16 digital output channels
Output type ....................................... Sinking
Power-on output state ....................... Channels off
Output voltage (V0)........................... I0R0
External power supply
voltage range (Vsup)........................... 0–50 VDC
Continuous output current (I0)1, per channel
All channels on........................... 1.2 A max
Four channels on ........................ 2.5 A max
One channel on........................... 5 A max
1 Refer to the Safe Operating Current section for more information about safe
operating current.

NI 9478 Operating Instructions and Specifications 20 ni.com
Switched output current (10 kHz)1, per channel
All channels on........................... 1 A max
Four channels on ........................ 2 A max
One channel on........................... 4 A max
Switched output current (20 kHz)1, per channel
All channels on........................... 0.75 A max
Four channels on ........................ 1.67 A max
One channel on........................... 3.33 A max
Output impedance (R0) ..................... 50 mΩmax
Reversed-voltage protection ............. None
Number of current limit settings....... 2 (Limit A and Limit B)
Current limit range............................ 0–5.1 A
Current limit resolution..................... 8-bit, 20 mA per LSB
Current limit accuracy ......................130 mA + 3% of setting, max
1 Using up to 2 meters of cabling on each output channel. Refer to the Safe Operating
Current section for more information.