Measurement Computing CIO-DAS1601/12 User manual

CIO-DAS1601/12
CIO-DAS1602/12
CIO-DAS1602/16
ANALOG & DIGITAL I/O BOARD
for ISA BUS
Standard and -P5 versions
Revision 6
© Copyright November, 2000

LIFETIME WARRANTY
Every hardware product manufactured by Measurement Computing Corp. is warranted against defects in
materials or workmanship for the life of the product, to the original purchaser. Any products found to be
defective will be repaired or replaced promptly.
LIFETIME HARSH ENVIRONMENT WARRANTYTM
Any Measurement Computing Corp. product which is damaged due to misuse may be replaced for only
50% of the current price. I/O boards face some harsh environments, some harsher than the boards are
designed to withstand. When that happens, just return the board with an order for its replacement at only
50% of the list price. Measurement Computing Corp. does not need to profit from your misfortune. By
the way, we will honor this warranty for any other manufacture’s board that we have a replacement for!
30 DAY MONEY-BACK GUARANTEE
Any Measurement Computing Corp. product can be returned within 30 days of purchase for a full refund
of the price paid for the product being returned. If you are not satisfied, or chose the wrong product by
mistake, you do not have to keep it. Please call for a RMA number first. No credits or returns accepted
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These warranties are in lieu of all other warranties, expressed or implied, including any implied warranty
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even if Measurerment Computing Corp. has been notified in advance of the possibility of such damages.
MEGA-FIFO, the CIO prefix to data acquisition board model numbers, the PCM prefix to data acquisi-
tion board model numbers, PCM-DAS08, PCM-D24C3, PCM-DAC02, PCM-COM422, PCM-COM485,
PCM-DMM, PCM-DAS16D/12, PCM-DAS16S/12, PCM-DAS16D/16, PCM-DAS16S/16, PCI-
DAS6402/16, Universal Library, InstaCal, Harsh Environment Warranty and Measurement Computing
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Measurement Computing Corp. does not authorize any Measurement Computing Corp. product for use in
life support systems and/or devices without the written approval of the President of Measurement Com-
puting Corp. Life support devices/systems are devices or systems which, a) are intended for surgical
implantation into the body, or b) support or sustain life and whose failure to perform can be reasonably
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nents required, and are not subject to the testing required to ensure a level of reliability suitable for the
treatment and diagnosis of people.
HM CIO-DAS160#_1#.lwp

328.1 VOLTAGE DIVIDERS ........................................................ 32
8 ANALOG ELECTRONICS ....................................................... 317.2 CALIBRATING THE A/D & D/A CONVERTERS .................................. 317.1 REQUIRED EQUIPMENT ..................................................... 31
7 CALIBRATION AND TEST ...................................................... 306.1.15 BURST STATUS REGISTER ............................................... 306.1.14 DAS1600 MODE ENABLE REGISTER ...................................... 296.1.13 BURST MODE ENABLE REGISTER ........................................ 296.1.12 CONVERT DISABLE REGISTER ........................................... 276.1.11 24-bit DIGITAL I/O REGISTERS (not applicable on -P5 versions) ................. 276.1.10 PACER CLOCK DATA & CONTROL REGISTERS ............................. 266.1.9 PROGRAMMABLE GAIN CONTROL REGISTER / BURST RATE .................. 246.1.8 PACER CLOCK CONTROL REGISTER ....................................... 246.1.7 DMA, INTERRUPT & TRIGGER CONTROL ................................... 236.1.6 STATUS REGISTER ...................................................... 226.1.5 D/A REGISTERS ......................................................... 226.1.4 FOUR BIT DIGITAL I/O REGISTERS ........................................ 216.1.3 CHANNEL MUX SCAN LIMITS REGISTER ................................... 216.1.2 A/D DATA & CHANNEL REGISTERS (CIO-DAS1602/16) ........................ 206.1.1 A/D DATA & CHANNEL REGISTERS (CIO-DAS1600/12) ........................ 196.1 CONTROL & DATA REGISTERS .............................................. 19
6 REGISTER ARCHITECTURE .................................................... 175.3 ANALOG OUTPUTS ......................................................... 175.2.7 Isolated Grounds / Differential Inputs ........................................ 165.2.6 Isolated Grounds / Single-Ended Inputs ....................................... 155.2.5 Common Mode Voltage > +/-10V ............................................ 155.2.4 Common Mode Voltage < +/-10V / Differential Inputs ........................... 145.2.3 Common Mode Voltage < +/-10V / Single-Ended Inputs .......................... 145.2.2 Common Ground / Differential Inputs ........................................ 145.2.1 Common Ground / Single-Ended Inputs ....................................... 135.2 Wiring Configurations ......................................................... 115.1.2 System Grounds and Isolation ............................................... 85.1.1 Single-Ended and Differential Inputs .......................................... 85.1 ANALOG INPUTS ............................................................ 8
5 ANALOG CONNECTIONS ........................................................ 74.2 DIGITAL I/O CONNECTOR (NOT APPLICABLE TO -P5 VERSIONS) ................. 64.1 MAIN CONNECTOR DIAGRAM ................................................ 6
4 CONNECTOR PINOUTS .......................................................... 53.9 DT-CONNECT ............................................................... 53.8 BURST MODE GENERATOR ................................................... 43.7 PACER EDGE SELECT ........................................................ 33.6 BIPOLAR/UNIPOLAR AND GAIN SETTING ...................................... 33.5 D/A CONVERTER REFERENCE JUMPER BLOCK ................................. 23.4 8/16 CHANNEL SELECT ....................................................... 23.3 1/10 MHz XTAL JUMPER ...................................................... 23.2 DMA LEVEL SELECT ......................................................... 13.1 BASE ADDRESS ............................................................. 1
3 HARDWARE INSTALLATION .................................................... 1
2 SOFTWARE INSTALLATION ..................................................... 1
1 INTRODUCTION ................................................................
Table of Contents

369.2 CIO-DAS1602/16 ............................................................ 349.1 CIO-DAS1601/12 & CIO-DAS1602/12 ........................................... 34
9 SPECIFICATIONS .............................................................. 338.2 LOW PASS FILTERS .........................................................
Table of Contents

1 INTRODUCTION
The installation and operation of all CIO-DAS1600 series boards are very similar. Throughout this
manual we use CIO-DAS1600 as a generic designation for the CIO-DAS1601/12, CIO-DAS1602/12, and
CIO-DAS1600/16. When required, due to the differences in the boards, the specific board name is used.
2 SOFTWARE INSTALLATION
We recommend you install and run the InstaCalTM installation, test and calibration utility that was
shipped with your board prior to installing the board in your computer. InstaCalTM will show you how to
properly set the switches and jumpers on the board prior to physically installing the board in your
computer.
Refer to the Software Installation Manual for detailed instructions regarding the installation of the
InstaCalTM software.
3 HARDWARE INSTALLATION
The CIO-DAS1600 has a variety of switches and jumpers to set before installing the board in your
computer. By far the simplest way to configure your board is to use the InstaCalTM program provided as
part of your CIO-DAS1600 software package. InstaCalTM will show you all available options, how to
configure the various switches and jumpers to match your application requirements, and will create a
configuration file that your application software (and the Universal Library) will refer to so the software
you use will automatically know the exact configuration of the board.
Please refer to the Software Installation Manual regarding the installation and operation of InstaCalTM.
The following hard copy information is provided as a matter of completeness, and will allow you to set
the hardware configuration of the CIO-DAS1600 board if you do not have immediate access to
InstaCalTM and/or your computer.
3.1 BASE ADDRESS
Unless there is already a board in your system using
address 300 hex (768 decimal), leave the switches as they
are set at the factory.
In Figure 3-1, the CIO-DAS1600 is set at base address
300 hex. This means the DAS-16 compatible section of
the board is at 300 hex and the DIO-24 compatible
section of the board is at 700 hex. Figure 3-1. Base Address & Wait EN Switch
Note: Wait State Enable is typically not required. Leave the WAIT EN switch in the UP (not enabled)
position
1

3.2 DMA LEVEL SELECT
If you are installing the board in an old XT bus computer, DMA level 3 is
probably used by the hard disk controller. Set the DMA level switch
to level 1 position (Figure 3-2).
If you have a 386 or higher computer, the hard disk controller does
not use either DMA level 1 or 3 so either level can be selected. The
default level is level 1.
Figure 3-2. DMA Level Select Switch
There are other boards that use DMA levels. Some network boards do and so do some IEEE-488
interface boards. Check to see if you have other boards in your computer that use DMA channels 1 or 3.
3.3 1/10 MHz XTAL JUMPER
The 1/10 MHz XTAL jumper selects the frequency of the square wave
used as a clock by the A/D pacer circuitry. This pacer circuitry controls
the sample timing of the A/D. The output driving the A/D converter is
also available at the CTR 2 output pin on the main connector.
To maintain full compatibility with the original DAS-16, the
CIO-DAS1600 required a 1 MHz crystal oscillator. When the DAS-16
was redesigned, a faster 10MHz crystal was added. A jumper is
provided to maintain compatibility with older software. The
CIO-DAS1600 has the jumper because the DAS-16 has the jumper and
some existing software requires the jumper to be in the 1 MHz position
while other software requires a 10 MHz oscillator. The CIO-DAS1600
is shipped with the jumper in the 1 MHz position (Figure 3-3). Figure 3-3. 1 or 10 MHz Select Jumper
3.4 8/16 CHANNEL SELECT
The analog inputs of the CIO-DAS1600 can be configured as eight differential or 16 single-ended. Use
the single-ended input mode if you have more than eight analog
inputs to sample. Using the differential input mode allows up to
10 volts of common mode (ground loop) rejection and will
provide better noise immunity.
The CIO-DAS1600 comes from the factory configured for 16
single-ended inputs and the 8/16 switch is in the position shown in
Figure 3-4. Set it for the type and number of inputs you desire.
This switch is located under the metal shield. If you need access
to this switch, this shield may be removed by removing the two
screws on the back of the CIO-DAS1600. Figure 3-4. 8/16 Channel Select Switch
2
1
10
Default 1MHz Shown
CLK SEL
1
6/8 CHANNEL SELECT SWITCH
1
6-Channel Single-Ended Input
Mode Shown
1
68

3.5 D/A CONVERTER REFERENCE JUMPER BLOCK
The jumper block located near the center of the CIO-DAS1600 allows you to use the on board precision
voltage reference to select the output ranges of the digital to analog converters.
Analog output is provided by two 12-bit multiplying D/A converters. This type of converter accepts a
reference voltage and provides an output proportional to that. The proportion is controlled by the D/A
output code (0 to 4095). Each bit represents 1/4096 of full scale.
A precision −5V and −10V reference provide onboard D/A ranges of 0 to 5V, 0 to 10V, ±5V, ±10V.
Other ranges between 0V and 10V are available if you provide a precision voltage reference at pin 10 or
26 of the main connector.
When the DAC0 reference is supplied onboard, pin 26 of the 37 pin connector is unused and can be
employed as a simultaneous sample & hold trigger for use with the CIO-SSH16. To do so, place the
jumper between the two pins SH (Figure 3-5).
Figure 3-5. D/A Output Range Jumper Block
3.6 BIPOLAR/UNIPOLAR AND GAIN SETTING
The Bipolar or Unipolar configuration of the A/D converter is set by a switch (Figure 3-6). The switch
controls all A/D channels. Though you cannot run some channels bipolar and some unipolar, you can
measure a unipolar input in the bipolar mode. (e.g. you can monitor a 0 to 5V input with a ±5 V channel)
3

The input amplifier gain is controlled by a software programmed register located at BASE + B hex (11
decimal). The codes have different meaning for each board in the CIO-DAS1600 family. Refer to the
Register Architecture section for details on this register.
Figure 3-6. Bipolar/Unipolar Select Switch
3.7 PACER EDGE SELECT
The original Keithley MetraByte DAS-1600 was designed such that A/D conversion was initiated on the
falling edge of the convert signal. Neither the original DAS-16, nor any of the other DAS-16 derivative
converts on the falling edge. In fact, we are not aware of any A/D board that uses the falling edge to
initiate the A/D conversion.
When using the falling edge to start the conversion, the A/D may be falsely triggered by 8254 pacer clock
initialization glitching (easy to avoid but a real possibility in the DAS-1600). Converting on the falling
edge mode also may lead to timing differences if the CIO-DAS1600 board is being used as a replacement
for an older DAS16 series board.
Because using the falling edge trigger is undesirable, we have designed a jumper into the CIO-DAS1600
which allows you to choose which edge of the internal pacer signal
starts the A/D conversion. The jumper has no effect on an external
pacer signal (EXTCLOCK). The only reason we supply you the
option of a falling edge trigger is to provide complete compatibility
for those who have developed software for a DAS-1600 using the
AS-1600 drivers, AND, when using the CIO-DAS1600 with that
software you observe sample timing differences.
The CIO-DAS1600 is shipped with this jumper in the rising edge
position. Figure 3-7 to the right shows the edge selection options.
For compatibility with all third party packages, with all DAS-16
software and with CIO-DAS1600 software, leave this jumper in the
rising edge position Figure 3-7. Trigger Edge Select Jumper
AUXILIARY TRIGGER
There is a position for a header connector at the rear of the CIO-DAS1600. This connector provides the
same function as that found on the DAS-1600.
The A/D trigger signal can come from this connector, if installed. A jumper controls which pin the
trigger signal comes in from. We do not install this connector (nor is it installed on the DAS-1600).
4
TRIGGER EDGE SELECT
JUMPER BLOCK
J9
J9
Falling Edge A/D Trigger
DAS-1600 Method
Rising Edge A/D Trigger
DAS-16 Method
Default
Setting

3.8 BURST MODE GENERATOR
The burst mode generator is a clock signal that paces the A/D at the maximum multi-channel sample rate,
then periodically, performs additional maximum rate scans. In this way, the channel to channel skew
(time between successive samples in a scan) is minimized without taking a large number of undesired
samples (Figure 3-8).
.
Figure 3-8. Burst Mode Timing
The CIO-DAS1600 burst mode generator takes advantage of the fast A/D. The burst mode skew is 4 µs
between channels for the CIO-DAS160#/12. It is 13.3 µs for the CIO-DAS1602/16.
3.9 DT-CONNECT
There is no hardware configuration or installation required for DT-Connect. Software enables/disables
DT-Connect, and of course, you must have a DT-Connect equipped accessory board, (Measurement
Computing’s MEGA-FIFO, for example) before using the DT-Connect.
DT-CONNECT IN MASTER MODE ONLY
The CIO-DAS1600 implements DT-Connect MASTER MODE only. DT-Connect is always enabled and
is never busy. The ENABLED and BUSY signal levels are fixed in hardware. Since DT-Connect is
always enabled, any A/D conversions are always transferred out through the DT-Connect port regardless
of the bus transfer method specified. The CIO-DAS1600 can only operate in DT-Connect schemes where
it is the sole master.
To assure that DT-Connect is properly initialized prior to any A/D transfer, the DT-Connect DT-Request
handshake line is reset each time the programmable gain (Base + 11 decimal) register is written to.
Therefore, it is not possible to use the DT-Connect for A/D sets which involve setting the gain between
samples. This is not really a problem because any such scheme would be low speed and therefore store
data to disk, obviating the need to use DT-Connect to store data on the MEGA-FIFO.
Please see the data sheet on the MEGA-FIFO, a 128 million-sample buffer board as an example of a
DT-Connect accessory.
5
Ch0 Ch1 Ch2 Ch3 Ch0 Ch1 Ch2 Ch3
4uS Delay
Burst mode pacer fixed at
4 uS - CIO-DAS1600/12
13.3 uS - CIO-DAS1600/16
The length ofthe delay between
bursts is set by one of the internal
counters or may be controlled via
external trigger.

4 CONNECTOR PINOUTS
4.1 MAIN CONNECTOR DIAGRAM
The CIO-DAS1600 analog connector is a 37-pin “D”connector accessible from the rear of the PC
through the expansion back plate. An additional signal, SS&H OUT, is available at pin 26. It is required
when the CIO-SSH16 Simultaneous Sample and Hold card is used with a CIO-DAS1600 (Figure 4-1).
Figure 4-1. Main Analog Connector Pinout
The connector accepts female 37-pin D-type connectors, such as those on the C73FF-2, two foot cable
with connectors. If frequent changes to signal connections or signal conditioning is required we strongly
recommend purchasing the CIO-MINI37 screw terminal board and the mating C37FF-2 cable
6
LLGND 19
CH0 LOW / CH8 HIGH 18
CH1 LOW / CH9 HIGH 17
CH2 LOW / CH10 HIGH 16
CH3 LOW / CH11 HIGH 15
CH4 LOW / CH12 HIGH 14
CH5 LOW / CH13 HIGH 13
CH6 LOW / CH14 HIGH 12
CH7 LOW / CH15 HIGH 11
D/A 0 REF IN 10
D/A 0 OUT 9
-5V REF OUT 8
DIG GND 7
DIG IN 1 6
DIG IN 3 5
DIG. OUT 1 4
DIG. OUT 3 3
CTR 0 OUT 2
+5V PC BUS 1
37 CH0 HIGH
36 CH1 HIGH
35 CH2 HIGH
34 CH3 HIGH
33 CH4 HIGH
32 CH5 HIGH
31 CH6 HIGH
30 CH7 HIGH
29 LLGND
28 LLGND
27 D/A 1 OUT
26 D/A 1 REF IN / SS&H OUT
25 DIG IN 0 / TRIGGER
24 DIG IN 2 / CTR0 GATE
23 DIG OUT 0
22 DIG OUT 2
21 CTR 0 CLOCK IN
20 CTR 2 OUT
37 PIN CONNECTOR

4.2 DIGITAL I/O CONNECTOR (NOT APPLICABLE TO -P5 VERSIONS)
The digital I/O connector is mounted at the rear of the CIO-DAS1600 and will accept a 40-pin header
connector. The optional BP40-37 cable assembly brings the signals to a back plate with a 37-pin male
connector mounted in it. When connected through the BP40-37, the CIO-DAS1600 digital connector is
identical to the CIO-DIO24 connector. The pin out of the 40- pin digital connector and the BP40-37 cable
assembly are shown in Figure 4-2 below.
Figure 4-2. Digital 40-Pin Connector Pinout - BP40-37 Cable Assembly to Back Panel Pinout
7
PORT A 0
PORT A 1
PORT A 2
PORT A 3
PORT A 4
PORT A 5
PORT A 6
PORT A 7
PORT C 0
PORT C 1
PORT C 2
PORT C 3
PORT C 4
PORT C 5
PORT C 6
PORT C 7
GND
+5V
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
GND
+5V
GND
NC
GND
NC
GND
NC
GND
P
ORT B 0
P
ORT B 1
P
ORT B 2
P
ORT B 3
P
ORT B 4
P
ORT B 5
P
ORT B 6
P
ORT B 7
NC
NC
39 NC
37 GND
35 +5V
33 GND
31 NC
29 GND
27 NC
25 GND
23 NC
21 GND
19 PORT B0
17 PORT B1
15 PORT B2
13 PORT B3
11 PORT B4
9PORTB5
7PORTB6
5PORTB7
3NC
1 NC
NC 40
NC 38
PORT A0 36
PORT A1 34
PORT A2 32
PORT A3 30
PORT A4 28
PORT A5 26
PORT A6 24
PORT A7 22
PORT C0 20
PORT C1 18
PORT C2 16
PORT C3 14
PORT C4 12
PORT C5 10
PORT C6 8
PORT C7 6
GND 4
+5V 2

5 ANALOG CONNECTIONS
5.1 ANALOG INPUTS
Analog signal connection is one of the most challenging aspects of applying a data acquisition board. If
you are an Analog Electrical Engineer then this section is not for you, but if you are like most PC data
acquisition users, the best way to connect your analog inputs may not be obvious. Though complete
coverage of this topic is well beyond the scope of this manual, the following section provides some
explanations and helpful hints regarding these analog input connections. This section is designed to help
you achieve the optimum performance from your CIO-DAS1600 series board.
Prior to jumping into actual connection schemes, you should have at least a basic understanding of
Single-Ended/Differential inputs and system grounding/isolation. If you are already comfortable with
these concepts you may wish to skip to the next section (on wiring configurations).
5.1.1 Single-Ended and Differential Inputs
The CIO-DAS1600 provides either eight differential or 16 single-ended input channels.
Single-Ended Inputs
A single-ended input measures the voltage between the input signal and ground. In this case, in
single-ended mode the CIO-DAS1600 measures the voltage between the input channel and LLGND. The
single-ended input configuration requires only one physical connection (wire) per channel and allows the
CIO-DAS1600 to monitor more channels than the (2-wire) differential configuration using the same
connector and onboard multiplexor. However, since the CIO-DAS1600 is measuring the input voltage
relative to its own low level ground, single-ended inputs are more susceptible to both EMI
(Electro-Magnetic Interference) and any ground noise at the signal source. Figure 5-1a and 5-1b show the
theory of single-ended input configuration
Figure 5-1a. Single-Ended Voltage Input Theory
8
+
-
Input
Amp To A/D
Single-Ended Input
I/O
Connector
LL GND
CH IN

Figure 5-1b. Single-Ended Voltage Input Theory
Differential Inputs
Differential inputs measure the voltage between two distinct input signals. Within a certain range
(referred to as the common mode range), the measurement is almost independent of signal source to
CIO-DAS1600 ground variations. A differential input is also much more immune to EMI than a
single-ended one. Most EMI noise induced in one lead is also induced in the other, the input only
measures the difference between the two leads, and the EMI common to both is ignored. This effect is a
major reason there is twisted pair wire as the twisting assures that both wires are subject to virtually
identical external influence. Figure 5-2a and 5-2b below show a typical differential input configuration.
Figure 5-2a . Differential Input Theory
9
+
-
Input
Amp To A/D
LL GND
CH IN
~
12
Vs Vs + Vg2 - Vg1
Any voltage differential between grounds
g1 and g2 shows up as an error signal
at the input amplifier
Single-ended input with Common Mode Voltage
gg
+
-
Input
Amp To A/D
Differential Input
I/O
Connector
LL GND
CH High
CH Low

Figure 5-2b. Differential Input Theory
Before moving on to the discussion of grounding and isolation, it is important to explain the concepts of
common mode, and common mode range (CM Range). Common mode voltage is depicted in the diagram
above as Vcm. Though differential inputs measure the voltage between two signals, without (almost)
respect to the either signal’s voltages relative to ground, there is a limit to how far away from ground
either signal can go. Though the CIO-DAS1600 has differential inputs, it will not measure the difference
between 100V and 101V as 1 Volt (in fact the 100V would destroy the board!). This limitation or
common mode range is depicted graphically in Figure 5-3. The CIO-DAS1600 common mode range is
+/- 10 Volts. Even in differential mode, no input signal can be measured if it is more than 10V from the
board’s low level ground (LLGND).
Figure 5-3. Common Mode Range
10
+
-
Input
Amp To A/D
Differential
Input
LL GND
CH High
CH Low
~
Vs Vs
Vcm
Common Mode Voltage (Vcm) is ignored
by differential input configuration. However,
note that Vcm + Vs must remain within
the amplifier’s common mode range of ±10V
Vcm = Vg2 - Vg1 gg1 2
+1V
+2V
+3V
+4V
-10V
+5V
-9V
+6V
-8V
+7V
-7V
+8V
-6V
+9V
-5V
+10V
-4V
+11V
-3V
+12V
-2V
+13V
-1V
Gray area represents common mode ran
Both V+ and V- must always remain withi
the common mode range relative to LL G
Vcm
With Vcm= +5VDC,
+Vs must be less than +5V, or the common mode range will be exceeded (>+10V)

5.1.2 System Grounds and Isolation
There are three scenarios possible when connecting your signal source to your CIO-DAS1600 board.
1. The CIO-DAS1600 and the signal source have the same (or common) ground. This signal
source can be connected directly to the CIO-DAS1600.
2. The CIO-DAS1600 and the signal source have an offset voltage between their grounds (AC
and/or DC). This offset it commonly referred to a common mode voltage. Depending on the magnitude
of this voltage, it may or may not be possible to connect the CIO-DAS1600 directly to your signal
source. We will discuss this topic further in a later section.
3. The CIO-DAS1600 and the signal source already have isolated grounds. This signal source
can be connected directly to the CIO-DAS1600.
Which system do you have?
Try the following experiment. Using a battery powered voltmeter*, measure the voltage (difference)
between the ground signal at your signal source and at your PC. Place one voltmeter probe on the PC
ground and the other on the signal source ground. Measure both the AC and DC Voltages.
*If you do not have access to a voltmeter, skip the experiment and take a look a the following three
sections. You may be able to identify your system type from the descriptions provided.
If both AC and DC readings are 0.00 volts, you may have a system with common grounds. However,
since voltmeters will average out high frequency signals, there is no guarantee. Please refer to the section
below titled Common Grounds.
If you measure reasonably stable AC and DC voltages, your system has an offset voltage between the
grounds category. This offset is referred to as a Common Mode Voltage. Please be careful to read the
following warning and then proceed to the section describing Common Mode systems.
WARNING
If either the AC or DC voltage is greater than 10 volts, do not connect the
CIO-DAS1600 to this signal source. You are beyond the boards usable common mode
range and will need to either adjust your grounding system or add special Isolation
signal conditioning to take useful measurements. A ground offset voltage of more
than 30 volts will likely damage the CIO-DAS1600 board and possibly your computer.
Note that an offset voltage much greater than 30 volts will not only damage your
electronics, but it can also be hazardous to your health.
This is such an important point, that we will state it again. If the voltage between the
ground of your signal source and your PC is greater than 10 volts, your board will not
take useful measurements. If this voltage is greater than 30 volts, it will likely cause
damage, and can represent a serious shock hazard! In this case you will need to either
reconfigure your system to reduce the ground differentials, or purchase and install
special electrical isolation signal conditioning.
If you cannot obtain a reasonably stable DC voltage measurement between the grounds, or the voltage
drifts around considerably, the two grounds are most likely isolated. The easiest way to check for
11

isolation is to change your voltmeter to it’s ohm scale and measure the resistance between the two
grounds. It is recommended that you turn both systems off prior to taking this resistance measurement. If
the measured resistance is more than 100 Kohm, it’s a fairly safe bet that your system has electrically
isolated grounds.
Systems with Common Grounds
In the simplest (but perhaps least likely) case, your signal source will have the same ground as the
CIO-DAS1600. This would typically occur when providing power or excitation to your signal source
directly from the CIO-DAS1600. There may be other common ground configurations, but it is important
to note that any voltage between the CIO-DAS1600 ground and your signal ground is a potential error
voltage if you set up your system based on a common ground assumption.
As a safe rule of thumb, if your signal source or sensor is not connected directly to an LLGND pin on
your CIO-DAS1600, it’s best to assume that you do not have a common ground even if your voltmeter
measured 0.0 Volts. Configure your system as if there is ground offset voltage between the source and
the CIO-DAS1600. This is especially true if you are using either the CIO-DAS1600/16 or the
CIO-DAS1600/12 at high gains, since ground potentials in the sub-millivolt range will be large enough to
cause A/D errors, yet will not likely be measured by your hand-held voltmeter.
Systems with Common Mode (ground offset) Voltages
The most frequently encountered grounding scenario involves grounds that are somehow connected, but
have AC and/or DC offset voltages between the CIO-DAS1600 and signal source grounds. This offset
voltage may be AC, DC or both and can be caused by a wide array of phenomena including EMI pickup,
resistive voltage drops in ground wiring and connections, etc. Ground offset voltage is a more
appropriate term to describe this type of system, but since our goal is to keep things simple, and help you
make appropriate connections, we’ll stick with our somewhat loose usage of the phrase Common Mode.
Small Common Mode Voltages
If the voltage between the signal source ground and CIO-DAS1600 ground is small, the combination of
the ground voltage and input signal will not exceed the ’CIO-DAS1600’s +/-10V common mode range,
(i.e. the voltage between grounds, added to the maximum input voltage, stays within +/-10V), This input
is compatible with the CIO-DAS1600 and the system can be connected without additional signal
conditioning. Fortunately, most systems will fall in this category and have a small voltage differential
between grounds.
Large Common Mode Voltages
If the ground differential is large enough, the ’CIO-DAS1600’s +/- 10V common mode range will be
exceeded (i.e. the voltage between CIO-DAS1600 and signal source grounds, added to the maximum
input voltage you’re trying to measure exceeds +/-10V). In this case the CIO-DAS1600 cannot be
directly connected to the signal source. You will need to change your system grounding configuration or
add isolation signal conditioning. (Please look at our ISO-RACK and ISO-5B-series products to add
electrical isolation, or give our technical support group a call to discuss other options.)
12

NOTE
Relying on the earth prong of a 120VAC for signal ground connections is not advised..
Different ground plugs may have large and potentially even dangerous voltage
differentials. Remember that the ground pins on 120VAC outlets on different sides of
the room may only be connected in the basement. This leaves the possibility that the
“ground” pins may have a significant voltage differential (especially if the two
120VAC outlets happen to be on different phases.)
CIO-DAS1600 and signal source already have isolated grounds
Some signal sources will already be electrically isolated from the CIO-DAS1600. The diagram below
shows a typical isolated ground system. These signal sources are often battery powered, or are fairly
expensive pieces of equipment (since isolation is not an inexpensive proposition), isolated ground
systems provide excellent performance, but require some extra effort during connections to assure
optimum performance is obtained. Please refer to the following sections for further details.
5.2 Wiring Configurations
Combining all the grounding and input type possibilities provides us with the following potential
connection configurations. The combinations along with our recommendations on usage are shown in
Table 5-1 below.
Table 5-1. Input vs. Grounding Recommendations
Ground Category Input Configuration Our Recommendation
RecommendedDifferential Inputs
Already Isolated
Grounds
AcceptableSingle-ended InputsAlready Isolated Grounds
Unacceptable without
adding Isolation
Differential Inputs
Common Mode
Voltage > +/-10V
Unacceptable without
adding Isolation
Single-Ended Inputs
Common Mode
Voltage > +/- 10V
RecommendedDifferential Inputs
Common Mode
Voltage < +/-10V
Not RecommendedSingle-Ended Inputs
Common Mode
Voltage < +/-10V
AcceptableDifferential InputsCommon Ground
RecommendedSingle-Ended InputsCommon Ground
The following sections depicts recommended input wiring schemes for each of the eight possible input
configuration/grounding combinations.
13

5.2.1 Common Ground / Single-Ended Inputs
Single-ended is the recommended configuration for common ground connections. However, if some of
your inputs are common ground and some are not, we recommend you use the differential mode. There is
no performance penalty (other than loss of channels) for using a differential input to measure a common
ground signal source. However the reverse is not true. Figure 5-4 below shows a recommended
connection diagram for a common ground / single-ended input system
Figure 5-4. Common Ground / Single-Ended Inputs
5.2.2 Common Ground / Differential Inputs
The use of differential inputs to monitor a signal source with a common ground is a acceptable
configuration though it requires more wiring and offers fewer channels than selecting a single-ended
configuration. Figure 5-5 below shows the recommended connections in this configuration.
Figure 5-5. Common Ground / Differential Inputs
14
+
-
Input
Amp To A/D
A/D Board
I/O
Connector
LL GND
CH IN


Signal
Source with
Common Gnd
Optional wire
since signal source
and A/D board share
common ground
Signal source and A/D board
sharing common ground connected
to single-ended input.
+
-
Input
Amp To A/D
A/D Board
I/O
Connector
LL GND
CH High
CH Low


Signal
Source with
Common Gnd
Optional wire
since signal source
and A/D board share
common ground
Required connection
of LL GND to CH Low
Signal source and A/D board
sharing common ground connected
to differential input.

5.2.3 Common Mode Voltage < +/-10V / Single-Ended Inputs
This is not a recommended configuration. In fact, the phrase common mode has no meaning in a
single-ended system and this case would be better described as a system with offset grounds. You can try
this configuration, no system damage should occur and you may receive acceptable results.
5.2.4 Common Mode Voltage < +/-10V / Differential Inputs
Systems with varying ground potentials should always be monitored in the differential mode. Care is
required to assure that the sum of the input signal and the ground differential (referred to as the common
mode voltage) does not exceed the common mode range of the A/D board (±10V on the CIO-DAS1600).
Figure 5-6 below show recommended connections in this configuration.
Figure 5-6. Common Mode Voltage < +/-10V / Differential Inputs
5.2.5 Common Mode Voltage > +/-10V
The CIO-DAS1600 will not directly monitor signals with common mode voltages greater than +/-10V.
You will either need to alter the system ground configuration to reduce the overall common mode
voltage, or add isolated signal conditioning between the source and your board. See Figure 5-7 and 5-8
below.
Figure 5-7. Common Mode Voltage > +/-10V. Single-Ended Input
15
+
-
Input
Amp To A/D
A/D Board
I/O
Connector
LL GND
CH High
CH Low


Signal Source
with Common
Mode Voltage
Signal source and A/D board
with common mode voltage
connected to a differential input.
GND
The voltage differential
between these grounds,
added to the maximum
input signal must stay
within +/-10V
System with a Large Common Mode Voltage,
Connected to a Single-Ended Input
I/O
Connector
+
-
Input
Amp To A/D
LL GND
CH IN
A/D Board


L
arge common
mode voltage
between signal
source & A/D board
GND
Isolation
Barrier
When the voltage difference
between signal source and
A/D board ground is large
enough so the A/D board’s
common mode range is
exceeded, isolated signal
conditioning must be added.

Figure 5-8. Common Mode Voltage > +/-10V. Differential Input
5.2.6 Isolated Grounds / Single-Ended Inputs
Single-ended inputs can be used to monitor isolated inputs, though the use of the differential mode will
increase you system’s noise immunity. Figure 5-9 below shows the recommended connections is this
configuration.
Figure 5-9. Isolated Grounds / Single-Ended Input
16
System with a Large Common Mode Voltage,
Connected to a Differential Input


L
arge common
mode voltage
between signal
source & A/D board
GND
Isolation
Barrier
When the voltage difference
between signal source and
A/D board ground is large
enough so the A/D board’s
common mode range is
exceeded, isolated signal
conditioning must be added.
+
-
Input
Amp To A/D
A/D Board
I/O
Connector
LL GND
CH High
CH Low
10 K
10K is a recommended value. You may short LL GND to CH Low
instead, but this will reduce your system’s noise immunity.
Isolated Signal Source
Connected to a Single-Ended Input
I/O
Connector
+
-
Input
Amp To A/D
LL GND
CH IN
A/D Board


Isolated
signal
source