National Instruments SCXI-1305 User manual

National Instruments™,ni.com
™, and SCXI™are trademarks of National Instruments Corporation. Product and company names mentioned herein are
trademarks or trade names of their respective companies.
322313B-01 ©Copyright 1999, 2000 National Instruments Corp. All rights reserved. December 2000
INSTALLATION GUIDE
SCXI -1305 AC/DC COUPLING BNC
TERMINAL BLOCK
This guide describes how to install and use your SCXI-1305 AC/DC
coupling BNC terminal block.
Introduction
The SCXI-1305 is a shielded terminal block with BNC and SMB
connectors that you can connect to the SCXI-1120/D, SCXI-1121,
SCXI-1125, SCXI-1126, SCXI-1140, or SCXI-1141/1142/1143 input
connectors. You can configure each SCXI-1305 channel to AC- or
DC-couple a signal to an SCXI module. Each channel can
ground-reference a floating signal with a bias resistor.
The terminal block has eight BNC and one SMB connector for easy
connection. The eight BNCs are for signal connections to the eight module
inputs. The SMB provides access to module digital signals, HOLDTRIG
for the SCXI-1140, and OUTCLK and EXTCLK for the
SCXI-1141/1142/1143. These signals are not active on the SCXI-1120/D,
SCXI-1121, SCXI-1125, and SCXI-1126.
Caution The SCXI-1305 limits the maximum common-mode voltage of the
SCXI-1120/D, SCXI-1121, SCXI-1125, and SCXI-1126 to 42 Vpeak or DC. Exceeding this
level may injure you. National Instruments is not liable for damage or injuries resulting
from improper connection.
What You Need to Get Started
To set up and use your SCXI-1305 terminal block, you need the following
items:
❑SCXI-1305 terminal block
❑SCXI-1305 AC/DC Coupling BNC Terminal Block Installation Guide
™

SCXI-1305 Installation Guide 2 ni.com
❑SCXI chassis
❑One of the following modules:
– SCXI-1120/D
– SCXI-1121
– SCXI-1125
– SCXI-1126
– SCXI-1140
– SCXI-1141/1142/1143
❑Number 1 and 2 Phillips-head screwdrivers
❑1/8 in. flathead screwdriver
❑Long-nose pliers
❑Wire cutter
❑Wire insulation stripper
❑SMB cable
❑BNC cable
Conventions
The following conventions are used in this guide:
This icon denotes a note, which alerts you to important information.
This icon denotes a caution, which advises you of precautions to take to
avoid injury, data loss, or a system crash.
italic Italic text denotes variables, emphasis, a cross reference, or an introduction
to a key concept. This font also denotes text that is a placeholder for a word
or value that you must supply.
monospace Text in this font denotes text or characters that you should enter from the
keyboard, sections of code, programming examples, and syntax examples.
This font is also used for the proper names of disk drives, paths, directories,
programs, subprograms, subroutines, device names, functions, operations,
variables, filenames and extensions, and code excerpts.

©National Instruments Corporation 3 SCXI-1305 Installation Guide
Safety Information
Caution Do not operate the device in an explosive atmosphere or where there may be
flammable gases or fumes.
Do not operate damaged equipment. The safety protection features built into this device
can become impaired if the device becomes damaged in any way. If the device is damaged,
turn the device off and do not use it until service-trained personnel can check its safety.
If necessary, return the device to National Instruments for service and repair to ensure that
its safety is not compromised.
Do not operate this equipment in a manner that contradicts the information specified in this
document. Misuse of this equipment could result in a shock hazard.
Do not substitute parts or modify equipment. Because of the danger of introducing
additional hazards, do not install unauthorized parts or modify the device. Return the
device to National Instruments for service and repair to ensure that its safety features are
not compromised.
Yo u must insulate all of your signal connections to the highest voltage with which the
SCXI-1305 can come in contact.
Connections, including power signals to ground and vice versa, that exceed any of the
maximum signal ratings on the SCXI device can create a shock or fire hazard, or can
damage any or all of the boards connected to the SCXI chassis, the host computer, and the
SCXI device. National Instruments is not liable for any damages or injuries resulting from
incorrect signal connections.
Clean the module and accessories by brushing off light dust with a soft non-metallic brush.
Remove other contaminants with a stiff non-metallic brush. The unit must be completely
dry and free from contaminants before returning it to service.
The terminal block must be used with a UL-listed SCXI chassis.

SCXI-1305 Installation Guide 4 ni.com
Configuring Floating or Ground-Referenced Signals
Before you install and use your terminal block, you need to determine what
type of signal sources are in your SCXI system. Signal sources are either
floating or ground-referenced.
Afloating source is not connected in any way to the building ground
system and has an isolated ground-reference point that you cannot assume
to be at the same potential as any other ground. Examples of floating
sources include transformers, insulated thermocouples, optical isolators,
isolation amplifiers, and battery-powered devices.
Aground-referenced source is connected to the building ground and shares
a common ground with the DAQ device, assuming that your computer is
connected to the building power supply. Examples of ground-referenced
signals are the nonisolated outputs of any devices that plug into the building
power supply, such as signal generators and power supplies. Isolated
outputs do not constitute ground-referenced sources; you should treat them
as floating sources.
You should reference an input signal to ground at only one point. Therefore,
do not reference the input of a differential amplifier module to ground if the
signal source is already ground-referenced. If you are measuring a floating
source, reference the input to ground.
To ground-reference a floating signal for each channel, use the switch
settings shown in Table 1. Each channel has one switch with two positions
as follows:
•Use the F position with floating signal sources. Setting one of these
switches to the F position connects a 100 kΩresistor between the
negative input for the channel and analog ground. This resistor
supplies the necessary reference to ground for the channel. Do not
use this position with the SCXI-1120/D, SCXI-1121, SCXI-1125, or
SCXI-1126.
•Use the G position with ground-referenced sources. Setting the switch
to the G position disconnects the resistor from the signal path. Always
use this position on the SCXI-1120/D, SCXI-1121, SCXI-1125, and
SCXI-1126.

©National Instruments Corporation 5 SCXI-1305 Installation Guide
Refer to Figure 2 for the floating and ground-referenced signal
configuration switch locations.
Configuring the Channels for AC or DC Coupling
You can configure each channel for either AC or DC coupling using the
switch settings shown in Table 2. Change any switch settings before you
connect signals to the terminal block. Each channel requires you to set two
switches in the same position for the coupling circuitry to operate properly.
Configure the channels as follows:
•For AC coupling, set both switches to the AC position. The AC
position places single-pole highpass filters in the paths of both the
positive and negative inputs for the channel. Each filter consists of a
1 µF DC blocking capacitor and a 1 MΩresistor to analog ground1,
giving a –3 dB cutoff frequency of 0.16 Hz. The capacitors can block
up to 50 VDC; however, voltages applied to the terminal block must
never exceed ±42 VDC.
•For DC coupling, set both switches to the DC position. DC coupling
removes the filters from the signal paths and connects the BNCs
directly to the module inputs. Always use this position on the
SCXI-1121 excitation channels.
Table 1. Floating and Ground-Referenced Signal Configuration
Switch Position Description
References floating signals to
ground.
Disconnects ground-reference
resistor; use for signals that are
already ground-referenced
(factory setting). This is the
SCXI-1120/D, SCXI-1121,
SCXI-1125, and SCXI-1126
position.
1For the SCXI-1120/D, SCXI-1121, SCXI-1125, and SCXI-1126, there is an effective 2 MΩresistor instead of two 1 MΩ
resistors. This 2 MΩresistor is referenced to the negative input of the SCXI-1120/D, SCXI-1121, SCXI-1125, and
SCXI-1126 instead of ground to maintain the SCXI-1120/D, SCXI-1121, SCXI-1125, and SCXI-1126 isolation.
F
G
F
G

SCXI-1305 Installation Guide 6 ni.com
Refer to Figure 2 for the AC/DC coupling configuration switch locations.
Configuring the Clock
Due to space limitations, a jumper, W1, inside the terminal block is used to
select which clock goes to the SMB connector. See Figure 2 for the location
of jumper W1. Refer to your SCXI-1140 User Manual or
SCXI-1141/1142/1143 User Manual for the use of these clocks.
Connecting the Signals
Note Refer to the Safety Information section before removing equipment covers or
connecting or disconnecting any signal wires.
To connect the signal to the terminal block, perform the following steps,
referringtoFigures1and2asnecessary:
1. Unscrew the top cover screws and remove the top cover.
2. Configure each of the AC/DC coupling and ground-referencing
switches, depending on the signal you are measuring and the SCXI
module you are using. The top set of switches (S1, S2, and S3)
corresponds to input channel 0, the next set down (S4, S5, and S6)
corresponds to input channel 1, and so on. The bottom set of switches
(S22, S23, and S24) corresponds to input channel 7.
Table 2. AC/DC Coupling Configuration
Switch Position Description
Use for AC coupling of the input
signal.
Use for DC coupling of the input
signal (factory setting). Use this
position for the SCXI-1121
excitation channels.
AC
DC
AC
DC

©National Instruments Corporation 7 SCXI-1305 Installation Guide
3. If using your SCXI-1305 with an SCXI-1140 or
SCXI-1141/1142/1143, configure the SMB connector function
(jumper W1).
4. Reinstall the top cover and tighten the top cover screws.
5. Connect your signal wires to the BNC and SMB connectors. Signal
names printed in black are for the SCXI-1120/D, SCXI-1125,
SCXI-1126, SCXI-1140, and SCXI-1141/1142/1143. Signal names
printed in blue are for the SCXI-1121. When connecting your signals
to the SCXI-1305, follow the labeling on the SCXI-1305 for the
appropriate module.
Figure 1. SCXI-1305 Parts Locator Diagram
1 Mating Connector 2Thumbscrew 3 Top Cover Screws 4TopCover
4
3
1
2
HOLD/CLK
!
M
A
X
I
N
P
U
T
4
2
V
O
L
T
S
C
H
4
C
H
3
C
H
2
C
H
1
C
H
0
C
H
7
C
H
6
C
H
5
C
H
2
E
X
1
C
H
1
E
X
0
C
H
0
E
X
3
C
H
3
E
X
2

SCXI-1305 Installation Guide 8 ni.com
Figure 2. SCXI-1305 Signal Connections
Note Signal names printed in black (the first name in the pair) are for the SCXI-1120/D,
SCXI-1125, SCXI-1126, SCXI-1140, and SCXI-1141/1142/1143. Signal names printed in
blue (the second name in the pair) are for the SCXI-1121.
1 Jumper W1
2 Channel 0 Switches
3 Channel 1 Switches
4 Channel 2 Switches
5 Channel 3 Switches
6 Channel 4 Switches
7 Channel 5 Switches
8 Channel 6 Switches
9 Channel 7 Switches
10 Serial Number
11 AC/DC Coupling Switches
12 Floating/Ground Reference Switches
13 SCXI-1121 Signal Connections
14 SCXI-1120/D, 1125, 1126,
1140, 1141/1142/1143
Signal Connections
15 SMB Connector
HOLD/CLK
!
M
A
X
I
N
P
U
T
4
2
V
O
L
T
S
C
H
4
C
H
3
C
H
2
C
H
1
C
H
0
C
H
7
C
H
6
C
H
5
C
H
2
E
X
1
C
H
1
E
X
0
C
H
0
E
X
3
C
H
3
E
X
2
2
1
12 11
3
4
5
6
7
8
9
10
14
15
13

©National Instruments Corporation 9 SCXI-1305 Installation Guide
Installing the Terminal Block
To connect the terminal block to the SCXI module front connector, perform
the following steps:
1. Connect the module front connector to its mating connector on the
terminal block.
2. Tighten the top and bottom thumbscrews on the back of the terminal
block to hold it securely in place.
Circuit Diagram
You do not need to read this section to operate the SCXI-1305. The circuit
diagram in Figure 3 is optional information that you can use if you want
more details about the SCXI-1305 circuitry. Figure 3 shows the circuitry
for one of the eight analog channels.
Figure 3. SCXI-1305 Circuit Diagram
1µF,
10%,
50V
1µF,
10%,
50V
BNC
Inputs
(open) G
(closed) F
Module
Inputs
+
–
DC
AC
DC
AC
A
A
ATies to analog ground on the SCXI-1140 and SCXI-1141/1142/1143.
On the SCXI-1120/D, SCXI-1121, SCXI-1125, and SCXI-1126,
it is left floating.

SCXI-1305 Installation Guide 10 ni.com
Specifications
All specifications are typical at 25 °C unless otherwise specified.
Electrical
Compatible modules
SCXI-1120/D...................................8 input channels
SCXI-1121.......................................4 input channels and
4 excitation output channels1
SCXI-1125.......................................8 input channels
SCXI-1126.......................................8 input channels
SCXI-1140.......................................8 input channels and
one external clock signal
SCXI-1141.......................................8 input channels and
two clock signals
SCXI-1142.......................................8 input channels and
two clock signals
SCXI-1143.......................................8 input channels and
two clock signals
Coupling .................................................DC or AC (selectable on
a per-channel basis using
slide switches)2
AC coupling circuitry
Corner frequency (–3 dB)................0.16 Hz
DC-rejection capacity......................±42 VDC
Input impedance (minimum)
Between CH+ and
CH– terminals ..........................2 MΩ
Between CH+ or CH–
terminal and ground .................1 MΩ3
1The excitation output channels must be configured for DC coupling.
2In instrumentation terminology, DC coupling means that both DC and AC signals are passed. AC coupling means that DC
signals are blocked and AC signals are passed.
3Does not apply to the SCXI-1120/D, SCXI-1121, SCXI-1125, or SCXI-1126.