Campbell SDM-IO16A User manual

09/2020
Copyright © 2020
Campbell Scientific, Inc.

Table of contents
1. Introduction 1
2. Specifications 2
2.1 General 2
2.2 Terminal specifications (output mode) 3
2.3 Terminal specifications (input mode) 3
2.4 Pulse counting specifications 4
3. Installation 6
3.1 Power considerations 6
3.2 Terminal connections 7
3.3 Address selection switches 8
4. Programming the data logger 10
4.1 General principles 10
4.2 SDMIO16() instruction 11
4.3 SDMCD16AC() instruction 13
4.4 SDMSpeed() instruction 14
4.5 Command codes for the SDMIO16() instruction 14
Appendix A. General principles of pulse and frequency measurements 20
A.1 Introduction 20
A.2 Frequency and duty cycle measurement range 20
A.3 Resolution of frequency measurements 21
A.4 Resolution of duty cycle measurements 21
A.5 Debounce filtering 22
A.6 Using the I/O line to trigger code to run on a data logger 23
Table of Contents - i

1. Introduction
The SDM-IO16A expands the digital input and output capability of Campbell Scientific data
loggers. It offers similar functionality to the control terminals of Campbell Scientific data loggers.
The SDM-IO16A (see FIGURE 1-1 (p. 2)) is a synchronously addressed peripheral. It has 16
input/output (I/O) terminals configurable for input or output which expand the number of
control terminals of the data logger. It is fully compatible with Campbell Scientific GRANITE-
series, CR6, CR3000, CR1000X, CR800-series, and CR1000 data loggers.
NOTE:
This manual provides information only for current CRBasic data loggers. For retired CRBasic
and Edlog data logger support, see a prior SDM-IO16 manual at
www.campbellsci.com/manuals.
When a terminal is configured as an input, it measures the logical state of the terminal, counts
pulses, measures the frequency of and determines the duty cycle of signals applied to the
terminal. In pulse counting mode there is also an option to enable switch debounce filtering so
the unit will accurately count switch closure events. The SDM-IO16A measures the frequency of
signals by measuring the time between pulses, thereby giving relatively high-resolution
measurements even for low frequency signals.
The module may also be programmed to generate a signal to the data logger when one or more
input signals change state, which can be used to trigger special code in the data logger. This is
known as an interrupt function, as it is similar to a technique supported in microprocessors.
When configured as an output, each terminal is set to 0 or 5V by the data logger. In addition to
being able to drive normal logic level inputs, when an output is set HIGH a ‘boost’ circuit allows
it to source a current of up to 133 mA (short-circuited to ground) at a reduced output voltage,
allowing direct control of low voltage valves, relays, or other components. Refer to graph (d)
Output voltage versus current output in FIGURE 2-1 (p. 5) to see the available current at different
voltages.
The SDM-IO16A is a synchronously addressed data logger peripheral. Data logger control
terminals 1, 2 and 3 are used to address the SDM-IO16A and exchange digital data with it. This
module uses advanced error checking techniques to ensure correct transmission of data to and
from the module. Up to fifteen SDM-IO16As may be addressed, making it possible to control a
maximum of 240 terminals from the first three data logger control terminals.
SDM-IO16A 16-Channel Input/Output Expansion Module 1

FIGURE 1-1. SDM-IO16A
2. Specifications
2.1 General
Compatible data loggers: GRANITE series, CR6, CR3000, CR1000X, CR800 series, and CR1000
Operating voltage: 12 VDC nominal (9 to 18 V)
Current drain at 12VDC: 600 µA typical standby (all terminals HIGH, no load, not pulse
counting)
Maximum (no output load): 3mA active with all 16 terminals
counting pulses at 2 KHz. Above the standby level, power
consumption is roughly proportional to input signal frequency and
number of terminals used. Maximum 4.5mA in high-speed mode
with 1-16 terminals counting pulses from 0Hz to 8KHz.
Current drawn from any output must be added to the standby level
to give the total current drain.
SDM port: 0/5 V logic level port compliant with the requirements of the
Campbell Scientific SDM protocol — this is designed for
connection to the data logger SDM port.
SDM-IO16A 16-Channel Input/Output Expansion Module 2

Operating temperature: –40 to 70 °C standard
Size: 188 x 64 x 22 mm (7.4 x 2.5 x 0.9 in)
Mounting: Mounting brackets have two holes at 177.8mm (7in) nominal
spacing. Mounting screws and plastic inserts suitable for use with
Campbell Scientific enclosures are also supplied.
Weight: 175 g (6.2 oz)
EMC status: Complies with EN61326:2013
Total SDM cable length: 6 m (20 ft) maximum recommended
2.2 Terminal specifications (output mode)
Output voltage (no load): Output ON/HIGH, nominal 5 V (minimum 4.5 V)
Output OFF/LOW, nominal 0 V (maximum 0.1 V)
Output sink current: Output will sink 8.6 mA from a 5 V source1
Output source current: Output will source 42 mA @ 3 V, 133 mA short-circuited to ground1
Max. output current:
(total for all outputs)
Limited by the 12 V supply.
2.3 Terminal specifications (input mode)
Input voltage: Input high, 4.0 V minimum threshold
Input low, 1.0 V maximum threshold
All inputs feature Schmitt triggered detectors.
Input protection: The input is clamped at –0.6V and +5.6V relative to ground via a
33Ω resistor1. This will withstand a continuous current flow of
200mA (including that which might be caused by accidentally
connecting directly to a 12V supply). To limit power dissipation and
damage at higher voltages than 12V, an external series current
limiting resistor is recommended.
Input impedance: The input is biased to +5 V relative to ground by a 100 kΩ resistor.
SDM-IO16A 16-Channel Input/Output Expansion Module 3

2.4 Pulse counting specifications
Maximum frequency: Low-speed mode 2.048KHz on all channels simultaneously with
switch debounce-mode set off, with a 50/50 duty cycle.
150Hz on all channels with default switch debounce timing
enabled and a 50/50 duty cycle2.
High-speed mode 8.192KHz on all channels simultaneously with
switch debounce-mode set off with a 50/50 duty cycle.
Minimum frequency: A frequency of 0Hz is measured if there are less than two high-to-
low signal transitions in the measurement interval.
Minimum pulse width: A pulse must stay high or low for a minimum of 244 μs (low-speed
mode) and 61.04 μs (high-speed mode) for a change of state or
pulse to be counted.
Switch debounce timing: With the default settings, a switch between the input and G must
remain closed for 3.17ms and then remain open for 3.17ms, to be
counted as a closure. The debounce is changeable from the user
program. In high-speed mode the debounce timing is one quarter
of this at 0.7925ms.
Accuracy: Internal clock accuracy ±0.01% (worst case) over the standard
temperature range of –40 to 70°C.2
Duty cycle resolution: Depends on frequency and measurement interval.2The average
duty cycle is measured for signals up to 4kHz (low-speed mode)
and 16KHz (high-speed mode).
Max measurement interval: For frequency or duty cycle measurements the data logger must
request a measurement at an interval no longer than 4096 seconds
(low-speed mode) and 1024 seconds (high-speed mode). Each
channel is measurable at different intervals, both for frequency and
duty cycle.
1If more detailed input/output characteristics are required, experienced users should consult the equivalent circuit
diagrams and graphs shown in FIGURE 2-1 (p. 5).
2See General principles of pulse and frequency measurements (p. 20) for a more detailed discussion.
SDM-IO16A 16-Channel Input/Output Expansion Module 4

(a) Input biasing and protection
(b) Output set ON (c) Output set OFF
(d) Output voltage versus current output
(e) Output voltage versus resistive load
FIGURE 2-1. Simplified equivalent terminal circuits and graphs of output voltage
SDM-IO16A 16-Channel Input/Output Expansion Module 5

3. Installation
For correct operation, the SDM-IO16A must be installed where there is no risk of water ingress or
condensation.
WARNING:
The order in which connections are made is critical. Always connect 12V first, followed by
ground, then the SDM control terminals.
The CABLE5CBL-L or a similar cable connects the data logger to the SDM-IO16A. For data logger
connections, see Table 3-1 (p. 6). Refer to FIGURE 3-2 (p. 8) for details of how to use the spring-
loaded terminals.
Table 3-1: Data logger to SDM-IO16A connections
Connection order SDM-IO16A Data logger
First 12 V 12 V on data logger or
external supply
Second ⏚G
Third
C1
C2
C3
C1
C2
C3
When using multiple SDM-IO16As, each SDM-IO16A is wired in parallel by connecting the data
logger connections of one SDM-IO16A to the next.
The transient protection of the SDM-IO16A relies on a low resistance path to earth. Ensure that
the ground return wire has as low a resistance as possible.
NOTE:
The total cable length connecting SDM-IO16As to SDM-IO16As and the data logger must not
exceed 6m (20ft). Total cable lengths in excess of 6m (20ft) will adversely affect
communications between the module and data logger.
3.1 Power considerations
For most applications, especially for pulse counting or status inputs, the data logger supply is
used to power the SDM-IO16A, as shown in FIGURE 3-1 (p. 7) (a).
SDM-IO16A 16-Channel Input/Output Expansion Module 6

When being used for control and outputting current the SDM-IO16A power requirements will be
large compared to most Campbell Scientific products when driving significant loads. For this type
of application an external power supply, as shown in FIGURE 3-1 (p. 7) (b), is recommended to
power the SDM-IO16A.
(a) Connection with data logger supply
(b) Connection with external supply
FIGURE 3-1. Connection block diagrams
3.2 Terminal connections
The SDM-IO16A uses spring-loaded terminals for each connection, which provide quick,
vibration resistant connections. The I/O terminals are labeled 1 to 16. A common ground terminal
is provided between each pair of I/O terminals.
Strip any insulation from the wire to give 7 to 9mm bare wire. Use a screwdriver to push against
the orange lever to open the terminal contact in either the top or front slot, as appropriate. Push
the wire into the opening, and, while holding it in position, release the screwdriver to close the
terminal contact. The wire will now be firmly held in place. See FIGURE 3-2 (p. 8).
SDM-IO16A 16-Channel Input/Output Expansion Module 7

NOTE:
It is not possible to reliably insert more than one solid-core wire into one terminal connector
unless the wires are soldered or clamped together. When inserting more than one stranded
wire, twist the bare ends together before insertion.
FIGURE 3-2. Use of terminal blocks
3.3 Address selection switches
Each SDM module must have a unique address. Address 15 (switch setting F) is reserved for the
SDMTrigger() instruction. The factory-set address is 00. Table 3-2 (p. 8) shows switch position
and the corresponding address. FIGURE 3-3 (p. 9) shows the position of the switch.
Table 3-2: SDM-IO16A SDM address settings
Switch Setting Decimal Address Base 4 Address
0 0 00
1 1 01
2 2 02
3 3 03
4 4 10
5 5 11
6 6 12
7 7 13
8 8 20
SDM-IO16A 16-Channel Input/Output Expansion Module 8