Campbell Scientific SDM-CVO4 User Manual
SDM-CVO4 4-Channel
Current/Voltage Output Module
Revision: 7/11
Copyright © 2001-2011
Campbell Scientific, Inc.
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SDM-CVO4 Table of Contents
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1. Introduction..................................................................1
2. Specifications ..............................................................2
2.1 General Specifications ..............................................................................2
2.2 Output Specifications................................................................................3
2.3 Isolation Specifications.............................................................................3
3. Power Considerations.................................................4
4. Installation....................................................................4
4.1 Connection to a Datalogger ......................................................................4
4.2 Output Device Connections......................................................................6
4.2.1 Voltage Output Mode .....................................................................6
4.2.2 Current Output Mode......................................................................6
4.2.3 Shield and Ground Connections .....................................................7
4.2.4 Output Terminal Connectors...........................................................8
4.3 Output Mode Setting ................................................................................8
4.4 SDM Address Setting ...............................................................................9
4.5 Safety Considerations .............................................................................10
5. General Principles of Use .........................................12
5.1 Voltage or Current Signaling..................................................................12
5.2 Providing Excitation Supplies to Sensors...............................................12
6. Datalogger Programming.......................................... 13
6.1 CRBasic SDMCVO4 Instruction............................................................14
6.2 SDMCVO4 Instruction Example............................................................15
6.3 SDMSpeed Instruction ...........................................................................16
6.4 Edlog Instruction 103 .............................................................................16
6.5 Edlog Program Examples .......................................................................18
6.5.1 Voltage and 0-20 mA Current Output Modes...............................18
6.5.2 Restricted Range Current Output Modes (4-20 mA) ....................20
6.5.3 Providing Isolated Power Supplies to Sensors..............................22
Figures
1. SDM-CVO4................................................................................................1
4-1. Use of the Spring-Loaded Terminal Blocks (Top Position)....................5
4-2. Use of the Spring-Loaded Terminal Blocks (Front Position)..................5
4-3. Location of Jumpers on Circuit Board ....................................................9
4-4. Address Selection Switch......................................................................10
i
SDM-CVO4 Table of Contents
Tables
4-1. Datalogger to SDM-CVO4 Connections ................................................ 4
4-2. Switch Position and Addresses............................................................. 10
6-1. Description of SDM Speed................................................................... 16
6-2. Description of Instruction 103.............................................................. 17
ii
SDM-CVO4 4-Channel Current/Voltage Output Module
The SDM-CVO4 is a synchronously addressed datalogger peripheral designed to allow the
datalogger to output variable voltage or current signals under program control.
FIGURE 1. SDM-CVO4 (shown without mounting brackets)
1. Introduction
The SDM-CVO4 expands the analog output capability of Campbell Scientific
dataloggers. Each output can be set to 0-10V or 0-20mA by the datalogger.
The output can be scaled and limited to 4-20mA by the datalogger program if
required by the application.
Typical applications will include driving remote ‘current-loop’ display units,
re-transmitting measured values to industrial control systems which have
current or high voltage inputs, sending control signals to valve controllers and
providing excitation voltages or currents to external sensors.
Each output is isolated both from the datalogger and the other channels on the
CVO4, thereby avoiding ground loop problems that might otherwise occur.
In the current mode the output can either act as a 2-wire current controller,
where the loop is powered from a remote voltage source, or it can be used to
generate a 0-20 mA current source using a voltage output derived from its own
power supply.
1
SDM-CVO4 4-Channel Current/Voltage Output Module
The SDM-CVO4 is a synchronously addressed datalogger peripheral. The
datalogger’s SDM ports are used to address the SDM-CVO4 and send out data
that defines the desired voltage/current output of each of the four channels.
The output levels are set by four values stored in variables or successive input
locations in the datalogger. A total of up to sixteen SDM-CVO4s or other
SDM peripherals may be connected and addressed from the same three ‘SDM’
ports.
NOTE
For the CR7, CR10(X), CR23X, and 21X dataloggers Instruction
103 is used to control the SDM-CVO4. This was introduced in
August 1988 for controlling SDM-AO4 functions. (The SDMAO4 is an older voltage-output-only peripheral.) Dataloggers
purchased before this date may use a different instruction.
The SDMCVO4 instruction is used with the CR800, CR850,
CR1000, CR3000, and CR5000.
2. Specifications
2.1 General Specifications
Compatible dataloggers: CR800, CR850, CR1000, CR3000, CR5000, and
Operating voltage: 12 VDC nominal (8 V to 16 V)
Current drain at 12V DC: Typical active quiescent current 27 or 54 mA,
CR7. Also compatible with many retired
dataloggers such as the CR10, 21X, and CR23X.
depending on operating mode (no load on output
ports). To estimate the total current, add the
quiescent current to the sum of all output currents
multiplied by 1.5.
2
E.g. if each port is at 10 mA output, the total =
54 + (1.5*4*10) = 114 mA. The device can be
shut down to <0.5 mA with all outputs off.
Maximum Total
SDM cable length: 600 ft (182 m) for the CR7; 20 ft (6 m) for other
dataloggers if the SDMSpeed Instruction is not
used. For our CR800, CR850, CR1000,
CR3000, and CR5000 dataloggers, cable lengths
longer than 20 ft may be acceptable if the
SDMSpeed instruction is used.
Operating temperature: -25°C to +50°C standard (-40 to 80°C optional)
Size: 176 mm wide x 111 mm high x 24 mm deep.
234 mm wide x 111 mm high x 24 mm deep
when fitted with brackets for mounting in
enclosure, etc. Mounting brackets have two holes
at 203.2 mm (8") spacing for screw fixings.
Weight: 370 g
EMC Status: Complies with EN55022-1:1998 and EN50082-
2.2 Output Specifications
Voltage Mode: Range: 0 – 10,000 mV
Accuracy (+23°C): ±0.02% of set voltage
Accuracy (-25 to +50°C): ±0.13% of set voltage
Current Mode: Range: 0 – 20 mA
Accuracy (+23°C): ±0.02% of full scale range
Typical Accuracy (-25° to +50°C): ±0.1% of full
SDM-CVO4 4-Channel Current/Voltage Output Module
1:1998
Resolution: 2.5 mV
Maximum Output Current: 30 mA per channel.
Minimum load current: 5 μA if output < 200 mV.
+ (± 2.5 mV).
+ (± 2.5 mV).
Resolution: 5 μA
Minimum output current (leakage): 5 μA at
+50°C.
+ (± 5 μA).
scale range + (± 5 μA).
Worst Case Accuracy (-25° to +50°C): ±0.15%
of full scale range + (±5 μA).
Minimum voltage drop across the internal current
regulating circuit: 2.5 V at 20 mA current flow.
Maximum voltage into I
When in current mode, the V
Please contact Campbell Scientific for the
2.3 Isolation Specifications
Design criteria: The unit has an internal isolation barrier and
Protection components are built-in, which will
Tested isolation: Each channel of each unit is tested for isolation
relative to channel
ground: 20 VDC.
an unregulated voltage source at 15 V nominal
(±10%), 30 mA maximum load.
accuracy specification on extended temperature
tested units.
components rated to provide signal isolation for
transients up to 1500 VAC (RMS), 2500 VDC
nominal. The isolation is between any output and
the SDM-CVO4 ground connection and between
individual output channels.
break down in a controlled fashion at voltages
close to this limit (see section 4.5, Safety Issues).
resistance at 500 VDC. Pass level > 10 MΩ.
d
terminal outputs
o
3
SDM-CVO4 4-Channel Current/Voltage Output Module
Maximum recommended
continuous operating voltage: 240 VAC RMS differential between an output
3. Power Considerations
The SDM-CVO4 power requirements are large compared to most Campbell
Scientific products, especially when driving significant loads. Care must be
taken to ensure that the power supply can cope with this higher demand.
Alkaline batteries are not recommended for long term applications.
The SDM-CVO4 has two internal power supplies, one for channels 1 and 2
and one for channels 3 and 4. It will only turn on the power supply for
channels 3 and 4 if sent an instruction that sets the output of those channels. If
channels 3 and 4 are not used the power consumption is approximately 20 mA
lower than when all outputs are used.
and datalogger ground - providing all issues
relating to local regulations for safe installation
and operation are followed (see section 4.5,
safety issues).
Where supported by the datalogger, and when the application allows it, the
SDM-CVO4 can be shut down to reduce its consumption to less than 0.5 mA.
In this state all outputs are switched off.
4. Installation
Prior to installing the device you need to set the output mode (current or
voltage) of each channel by positioning internal jumpers (see section 4.3). You
also need to set the SDM address of the module (see section 4.4) and
additionally consider any safety issues specific to the installation (see section
4.5).
4.1 Connection to a Datalogger
For datalogger connections, see Table 4-1, below.
TABLE 4-1. Datalogger to SDM-CVO4 Connections
Connection Order SDM-CVO4 Datalogger Function
First 12 V 12 V on datalogger or external supply Power
Second
or G
C1 SDM-C1 (CR3000, CR5000) or C1 (other dataloggers) Data
or G
Common Ground
C3 SDM-C3 (CR3000, CR5000) or C3 (other dataloggers) Enable
4
C2 SDM-C2 (CR3000, CR5000) or C2 (other dataloggers) Clock
Multiple SDM-CVO4s may be wired in parallel by connecting the SDM and
power connections from one SDM-CVO4 to the next.
SDM-CVO4 4-Channel Current/Voltage Output Module
NOTE
If the total cable length connecting SDM-CVO4s to
SDM-CVO4s, other SDMs and the datalogger exceeds 6 m, the
SDM baud rate may need to be reduced to ensure reliable
operation. Please contact Campbell Scientific for more
information.
The transient protection of the SDM-CVO4 relies on a low resistance path to
earth. Ensure that the ground return wire has as low a resistance as possible.
An additional G terminal is provided which can be connected directly to the
enclosure earth ground terminal to ensure this. Make sure the ground wire
from the SDM-CVO4 to the datalogger goes to its G terminal and not the AG
terminal.
The SDM-CVO4 uses spring-loaded terminal blocks for the connections to the
datalogger which provide quick, vibration resistant, connections. To attach
wires, insert a small screwdriver into either the top or front slot, as appropriate,
and push to open the terminal spring. Strip any insulation from the wire to give
7 to 9 mm bare wire. Push the wire into the opening, and, while holding it in
position, withdraw the screwdriver to release the spring. The wire will now be
firmly held in place. See Figures 4-1 and 4-2, below.
FIGURE 4-1. Use of the Spring-Loaded Terminal Blocks (Top Position)
FIGURE 4-2. Use of the Spring-Loaded Terminal Blocks (Front Position)
5
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