Tektronix AIM3A User manual

AIM3A

Analog Input Module

Introduction

The AIM3A analog input module accepts input signals of
flOOmV full scale through klOV full scale, and outputs a
signal of flOV full scale to the A/D converter module in
slot1 ofthedataacquisitionsystem.TheAIM3Acanaccept
32 single-ended (common ground) inputs, or 16 differen­tial (floating) inputs, or a mixture of both. All AEvl3A
functions,includinggainofxl,x10,andx100,areprogram­mable, permitting single-ended and differential inputs to
be intermixed with a different gain setting for each chan­nel. Full 16-bit precision results from the AIM3A’s low­noise instrumentation amplifier, linearity of 0.005%, and
attention to design, signal routing, and shielding. When
used with an AMMlA (AMMZ) A/D module, the AIM3A
will support 5OkHz (62.51d-12) measurements at any gain
and channel mix.

The AIM3A can be configured to accept current inputs by
installing appropriate current sensing resistors in the op.

tionalresistorlocationsprovidedon themodule.Theinput
signals are connected to removable screw terminal ships.
Alternately, a user-installed mass termination connector is
available for single-ended channels0-7 and 16-32, or differ­ential channels O-7. The mass termination connector uses
the pin out format of the Analog Devices 3B mainframe
ribbon cable connector to permit direct connection of the

AlM3A to a 3B signal conditioning subsystem.

Hardware Compatibility

The AIM3A can be used in slots 2 through 10 of the 500A
and 5OOP. Up to 9 AJM3A modules can be used in these
systemsforamaximumof3@4analoginputchannels(32SE
channels per AIM3A plus 16 SE channels on the AMMx in
slot 1). For best performance, analog modules should be
mounted in the lowest-numbered available slots. The
Alh43A can also be used in the option slot of the Model 575
or576forupto48analoginputchannels(32SEchannelson
the AlM3A plus 16 SE channels on the AMMx).

Document Number: 501-918-01 Rev. C / 3-92

Copyright 0 1989 Keithley Instruments, Inc., Cleveland, OH 44139 [phone] AIM3A-1

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AlM3A

Analog Input Module

Software Compatibility

Full control of the AIM3A requires software specifically
designed for this module. Keithley’s KDAC500 software
fully supports the AlM3A. If you are using third-party
software, be certain that the software fully supports the
AIM3A.

AIM3A Specifications

(Specifications apply for 18” to 28”C, 1 year)

Input channels: 16 differential or 32 single-ended, software

selectable

Input characteristics:

Input Protection: lt3OV max (powered), i-15V max

(unpowered)
Input Resistance: IOOMR
Input Bias Current: 5OnA

Software selectable gains:
Input range (+V):
Gain accuracy (% rdg): 0.05 0.01
Gain Nonlinearity (%): 0.005 0.005 0.005
Gain Tempco (%/“C): 0.002 0.002 0.002
Input offset @IV): 250 25 25
Offset Tempco QV/“C): 50 6
Input noise

@V RMS, 1OOKHz BW):
Settling time to .Ol%:
CMRR (DC to 60Hz): 70db 90db 100db

Power up conditions: gain = Xl, input channels = differ­ential, channel selected = channel 0.

xl
10 1

24 2.7 1.3
15ps 15ps 15la

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0.01

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Standard Connections

terminal block, first strip 3/16 of insulation from the end of
the wire which you want to attach. Loosen the desired
terminal screw on the block and insert the bare end of the
wire into the corresponding hole. Tighten the screw se­curely to compress the tab against the wire.

After you have attached all the desired signal wires to a
terminal block, replace the terminal block by lining it up
with the mating pins on the AIM3A and pressing it back
into place.

Alternate connections are available through the optional
cable mass termination connector Jll. Note that Jll con­nects only to channels 0 through 7 and 16 through 23 in

single-ended mode, or 0 through 7 in differential mode.
This connector is available from Scotch/3M as Part Num­ber 3429, and can be easily field-installed if it is needed.

Installation

All features and operating modes of the AlM3A module
are programmable with the exception of jumpers Wl and
W2 and resistor sockets J5 JlO. Jumpers Wl and W2
connect input low to module ground, and are normally left
in place. They may be removed for measurements where
remote ground sensing is needed. A jumper may be plain
wire, or may resemble a resistor.

Sockets J5 JlO are used for current sensing resistors, or for
ground reference resistors for some types of differential
measurements. These are special situations which are
covered under the “Applications” topic later in this man­ual.

The input connections to the AIM3A are made through
quick-disconnect terminal blocks Jl, J2, J3, and J4,or through
mass termination Jll.

A quick-disconnect terminal block can be removed from
the AlM3A to facilitate making connections. Pull the block
straight off the board with a firm, even pressure. Do not pry
the terminals with a screwdriver or sharp object, or you
may damage the circuit board.

Note that each individual terminal on a terminal block
consists of a small metal block with a hole and metal
compression tab within the hole. To make connections to a

CAUTION
Turn off power to the data acquisition system
before you insert or remove any module. To
minimize the possibility of EM1 radiation,
always operate the data acquisition system
with the cover in place and properly secured.

CAUTION
Make sure you have discharged any static

charges on your body before handling the
AIM3A. You can do this most easily by simply
touching the chassis of a computer or data

acquisition mainframe which is plugged into

AIM3A-3

AIM3A

Analog Input Module

a grounded, 3-wire outlet. Avoid touching
components or the card edge connector of the
module.

NOTE
Analog input modules should be placed in the
lowest-numbered availableslots. Thisposition­ing will provide the shortest distance to the
Analog Master Measurement module in slot 1,
and will also minimize any possibility of noise
pick-up from the power supply or other mod-

l&S.

For a compatible multi-slot data acquisition system (e.g.
Model 5OOA or 5OOP), remove the top cover of the system
by loosening the cover retaining screws located in the
upper corners of the rear panel. Slide the cover back about
one inch and then lift it off. Insert the AIM3A module in the
desired slot with the component side facing the system
power supply. Replace the system cover.

In a single-slot system such as the Model 575 or 576, first
attach the supplied right-angle bracket to the AIM3A (see
Figure 2). Install the AIM3A in the option slot, with the
component side of the board facing upward. Secure the
bracket to the rear panel of the system. Close and secure the
cover.

The AIM3A has a single, differential instrumentation am­plifier that amplifies all input signals, whether single­ended or differential. A differential amplifier responds
only to the difference in voltage between two signals
connected to its non-inverting (+) and inverting (-) inputs.
The common mode voltage is the average of the two input
voltages. The actual voltage at each input is not important
as long as the common voltage is within the common mode
range of the amplifier. The common mode range of thi
AIM3Awillnotbeexceededaslongasallinputsarewithin
the range -lOV to +lOV referenced to module ground.

For example, if the input to the (+) input is 9 Volts and the
input to the (-) input is 8 Volts, the amplifier will amplify
the +1 Volt difference signal and reject (ignore) the 8.5 volt
common mode signal at both inputs. The ability to reject
the8.5Volt commonsignal isreferred toasCommonMode
Rejection.

When the AIM3A amplifies a differential input signal, the

(+) input of the amplifier is connected to the selected (+)
channel on terminal block Jl or J3, and the (-) input of the
amplifier is connected to the corresponding (-) channel
terminal on J2 or J4. For example, if channel 2 and differen­tial mode are selected, the (+) input of the amplifier is
connected to pin 7 of Jl, and the (-1 input of the amplifier is
connected to pin 4 of JZ. As long as the voltage at either pin
is within +lO to -10 volts as measured to the module
ground (pin 10 of Jl and J3, or pin 1 of J2 and J4), the
amplifier will amplify the difference between the inputs.

End View Top View

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screws

Threaded Hole

screw

Bracket

‘@we 2. Model 575 Mounting Bracket

Applications

The following brief description of the AIM3A’s amplifier
circuitry will help you make the most effective use of the
module.

AIM3A-4

When the AIM3A amplifies a single-ended input signal,
the (+) input is connected to the selected channel on termi­nalblockJ1, J2, J3,or J4,and the (-1 inputisconnected toone
of common input low connections available on Jl, JZ, J3, or

14.

The jumpers Wl and W2 provide a user-removable con­nection between the input low connections and module
ground,andshouldnormallybeleftlnposition.TheAIM3A
amplifier will now amplify the voltage difference between
the selected (+) input terminal and module ground.

As an example, if channel 30 and single-ended mode are
selected, the (+) input of the amplifier is connected to pin
8 of J4, and the (-) input of the amplifier is connected to pin
10 of J4 (or pin 1 of J3, since these two pins are internally
connected). Pin 10 of J4 and pin 1 of J3 are jumpered to
module ground by WZ. The amplifier will amplify the
difference between pin 8 of J4 and pin 10 of J4.

AlM3A

Analog Input Module

There are two groups of 16 single-ended input channels,

and each group has its own (-) input connection. Single­ended channels 0 through 7 and 16 through 23 form one
group, with their (-) input connection brought to pin 1 of Jl
and pin 10 of J2. Jumper Wl connects this (-) input connec­tion to the module ground as supplied from the factory.
Single-ended channels 8 through 15 and 24 through 31
form the second group, with their (-) input connection
brought to pin 1 of J3 and pin 10 of J4. Jumper WZ connects
this (-1 input connection to the module ground as supplied
from the factory.

CAUTION
To minimize the possibility of EMI radiation,
use shielded cable for input signals. Connect
the shield to module ground, but do not con­nect the shield at the opposite cable end to
anything.Themaximuminputvoltageallowed
with module power on is i30 Volts, or 225
Volts with module power off. If any input
exceeds f10 Volts, all inputs will be lnopera­tive.

There are several choices for the method of connecting
inputs to the AIM3A. You must decide which method will
yield the best results for a given application. To achieve 16­bit performance, care must be taken to minimize error

sources caused by ground loops and shielding problems.

The guidelines for choosing connection methods are as

follows:

Single-ended Input, Local Ground Sensing. Using
Terminal Blocks

For input sources which can be grounded, but are not
connected to a ground of their own, the connections shown
in Figure 3 will give good results. The AIM3A provides the
ground connection for the input sources. Two possible
connectionsareshown.SourcesVOandVl haveindividual
cables going to each source. Up to 32 sources can be
connected to a single AIh43A in this way. Four input
common terminals are provided, one on each connector.
Connectall thewiresfromasingleinputsource to thesame
connector, asshownfor Jl inFigure3. SourcesV16andV17
show a cable with a single input common wire. This
connection method can be used for up to 16 sources in a
group where all the sources have one wire in common. The
sources in a single group must be connected to channels
which all use the same input common connection. There

are two input common connections, one for channels 0
through 7 and 16 through 23, and a second input common
connection for channels 8 through 15 and 24 through 31.

Single-ended Input, Remote Ground Sensing, Using

Terminal Blocks

Figure 4 shows four single-ended inputs connected to the
AIM3A using a remote ground sense line. All 16 single­ended inputs on Jl and J2 use a single ground sense line.
This method is useful when up to 16 voltage sources to be
measured are all located at a single remote location, with
one side of each signal source connected to ground at the
remote location. There may be a voltage difference be-

tween the ground at the remote location and the ground on
theAlM3A. This will cause an error in the voltage readings
if the connection in Figure 3 is used.

In Figure 4, the ground connection on theAIM3A is discon­nected by removing jumper Wl. The ground at the remote
location is carried to the AlM3A by the remote ground
sense wire. The AIM3A will measure the difference be­tween the remote signal, and the remote ground, and
eliminate the error caused by the difference in ground
voltage between it and the remote location. Two groups of
16 single-ended inputs can be wired this way, with the first
group using Jl, J2, and Wl, and the second group using J3,
J4, and W2 Refer also to Figures 10 and 11 later in this
manual.

Differential Inputs, Using Terminal Blocks

When there are multiple inputs with different ground

points, or the actual ground points are not known, the
differential input wiring can be used to prevent ground
loop errors and reject common mode noise. Figure 5 shows
two inputs connected as differential input channels 2 and

3. Either the (+) or the (-) input on any differential input
maybeconnected toground,orbothmay bediiferent from
ground. A restriction does exist, however. No input termi­nal on the AIM3A can be connected to a voltage beyond
+lOVor-10Vwithrespecttothe.4IM3Agroundreference.
If this happens, reading errors may occur on the channel
which is greater than 10 volts. At about +15 or -15 volts,
other channels will begin to read in error, and above +3OV
or -3OV, the AIM3A will be damaged.

When the AtM3A is used to measure a floating source, the
readings may appear noisy, or may fluctuate or rise until

they reach the maximum input permitted by the pro­grammed gains. This problem results where the floating
sourcehasnolow-impedancecurrentretumpathtoground.
Over a period of seconds to minutes, the input of the
AIM3A charges off the input signal until the common
mode voltage present at the input exceeds the allowable
level, and the module no longer functions properly. The

AIM3A-5

AIM3A

Analon Inaut Module

solution is to install a resistor for the affected channel from
inputlow toground.Thevalueof theresistormaybein the
range of 5k-lOOk, depending on the signal characteristics,

and should be determined empirically. These resistors can
be mounted on headers which are plugged into the avail-

able resistor sockets on the AEvf3A.

Notes:

1. Jumpers Wl and W2 must be in position. Wl connects input common for signals connected to Jl
and J2 to module ground. W2 connects input common of J3 and J4 to module ground.

2. All shields for singleended signals connected to Jl are attached to pin 10 of Jl, The shield input

on any connector is the right-most pin (Le. closest to the strain relief block of the AIM3A).

3. All input common lines for single-ended signals connected to Jl are attached to pin 1 of Jl, The
input common on any connector is the left-most pin (i.e. furthest from the strain relief block of the

AIM3A).

‘igure 3. Single-ended, Local Ground Sense, Using Terminal Blocks

AIM3A-6

AIM3A

Analog Input Module

Notes:

Wl Removed for remote

Ground sense with Jl & J2

I---

A+

Remote Ground

Sense

1. Jumpers Wi and or W2 must be removed for this mode of operation: Remove Wl if connections
Ji and J2 are used, or W2 if J3 or J4 are used.

2. The input common on any connector is the left-most pin (Le. furfhest from the strain relief block
of the AIM3A.

3. The shield input on any connector is the right-most pin (i.e. closest to the strain relief block of
the AIM3A.

‘igure 4. Single-ended, Remote Ground Sense, Using Terminals

AIM3A-7

AIM3A

Analog Input Module

Notes:

1. Jumpers Wl and or W2 may be in or out for this setup.

2. Input Common terminals have no effect for differential measurements.

3. The input common on any connector is the left-most pin (i.e. furthest from the strain relief
block of the AIM3A.

4. The shield input on any connector is the right-most pin (i.e. closest to the strain relief block of

the AIM3A.

igure 5. Differential Inputs, Using Terminal Blocks

Single-ended Inputs, Using Mass-termination

A location is provided near the strain relief block of the
AIh43A module for an optional mass termination connec-

tor Jl 1. Connector Jl 1 has its pins wired in parallel with the
connections on Jl and JZ, and provides a method for
quickly connecting up to 16 single-ended or 8 differential
signals to the AIM3A. The pin out of Jll is identical to that
of the Analog Devices 38 subsystem connector. When Jll
is used, the remaining input terminals on J3 and J4 of the
AIh43A may still be used in the usual fashion.

The pin out of Jll when used for single-ended inputs is
shown in Figure 6. The pin out of Jll when used with
differential inputs is shown in Figure 7. AU the input signal

connections previously described in Figures 3,4, and 5 can
be implemented with Jll. When Jll is used with the
AnalogDevices3B subsystem, the single-ended input with
remote ground sensing configuration is used, and Wl
must be removed.

AIh43A-8

AlM3A

Analog Input Module

Remove Wl if remote ground is used

To Input 6

To Input Common

Pinout of user-installed connector

( ~$$?$zd

Typical Input Wiring :

Remote ground,
if used

Notes:

1. Connector is user-installable. ScotchWM Part Number 3429.

2. Connectors J3 and J4 can be wired for other operating modes.

3. Jumper Wl connects input common to module ground. Remove Wl if remote ground sensing is
used

‘igure 6. Single-ended Hook-up, Using Mass Termination

AIM3A-9