Campbell AM16/32 User manual
INSTRUCTION MANUAL
AM16/32 Relay Multiplexer
Revision: 9/04
Copyright (c) 1987-2004
Campbell Scientific, Inc.
Warranty and Assistance
The AM16/32 RELAY MULTIPLEXER is warranted by CAMPBELL
SCIENTIFIC, INC. to be free from defects in materials and workmanship under
normal use and service for twelve (12) months from date of shipment unless
specified otherwise. Batteries have no warranty. CAMPBELL SCIENTIFIC,
INC.'s obligation under this warranty is limited to repairing or replacing (at
CAMPBELL SCIENTIFIC, INC.'s option) defective products. The customer
shall assume all costs of removing, reinstalling, and shipping defective products
to CAMPBELL SCIENTIFIC, INC. CAMPBELL SCIENTIFIC, INC. will
return such products by surface carrier prepaid. This warranty shall not apply
to any CAMPBELL SCIENTIFIC, INC. products which have been subjected to
modification, misuse, neglect, accidents of nature, or shipping damage. This
warranty is in lieu of all other warranties, expressed or implied, including
warranties of merchantability or fitness for a particular purpose. CAMPBELL
SCIENTIFIC, INC. is not liable for special, indirect, incidental, or
consequential damages.
Products may not be returned without prior authorization. The following
contact information is for US and International customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle repairs
for customers within their territories. Please visit www.campbellsci.com to
determine which Campbell Scientific company serves your country. To obtain
a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone (435) 753-2342. After an applications engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container.
CAMPBELL SCIENTIFIC's shipping address is:
CAMPBELL SCIENTIFIC, INC.
RMA#_____
815 West 1800 North
Logan, Utah 84321-1784
CAMPBELL SCIENTIFIC, INC. does not accept collect calls.
i
AM16/32 Relay Multiplexer
Table of Contents
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1. Function.......................................................................1
1.1 Typical Applications.................................................................................1
1.2 Compatibility............................................................................................2
2. Physical Description...................................................2
3. AM16/32 Specifications..............................................3
4. Operation.....................................................................5
4.1 The Control Terminals..............................................................................5
4.1.1 Reset................................................................................................6
4.1.2 Clock...............................................................................................6
4.1.3 Ground ............................................................................................7
4.1.4 Power Supply..................................................................................7
4.2 Measurement Terminals............................................................................8
4.2.1 COM Terminals ..............................................................................9
4.2.2 Sensor Input Terminals...................................................................9
5. Datalogger Programming.........................................10
5.1 Single Loop Instruction Sequence ..........................................................11
5.2 Multiple Loop Instruction Sequence.......................................................16
5.3 CR5000 and CR1000 Programming.......................................................18
5.3.1 CR5000 Programming ..................................................................19
5.3.2 CR1000 Programming ..................................................................20
5.4 General Programming Considerations....................................................22
6. Sensor Hook-up and Measurement Examples........22
6.1 Single-Ended Analog Measurement without Sensor Excitation.............22
6.2 Differential Analog Measurement without Sensor Excitation................23
6.3 Half Bridge Measurements .....................................................................24
6.3.1 Half Bridge Measurement with Completion Resistor at
Datalogger ......................................................................................24
6.3.2 Potentiometer Measurement..........................................................25
6.3.3 Four Wire Half Bridge with Measured Excitation........................25
6.4 Full Bridge Measurements......................................................................26
6.5 Full Bridges with Excitation Compensation...........................................27
AM16/32 Relay Multiplexer Table of Contents
ii
6.6 Thermocouple Measurement.................................................................. 28
6.6.1 Measurement Considerations ....................................................... 28
6.6.2 Single-ended Thermocouple Measurement.................................. 30
6.6.3 Differential Thermocouple Measurement..................................... 31
6.7 Mixed Sensor Types............................................................................... 31
6.7.1 Mixed Sensor Example: Soil Moisture Blocks and
Thermocouples............................................................................... 31
7. General Measurement Considerations....................34
8. Installation.................................................................34
8.1 Mounting Tabs....................................................................................... 35
8.2 Controlling Humidity............................................................................. 35
Appendices
A. AM16/32 Improvements over AM416 and AM32...A-1
Figures
1. AM16/32 Relay Multiplexer...................................................................... 3
2. AM16/32 Relay Actuation Time vs. Temperature and Battery Voltage..... 5
3. AM16/32 to Datalogger Power/Control Hookup....................................... 6
4. Power and Ground Connections for External Power Supply..................... 8
5. Typical AM16/32 to Datalogger Signal Hookup (4x16 Mode) ................. 9
6. SCWIN (Short Cut for Windows Program Builder) ................................ 10
7. Example “4X16” Mode Program Loops for CR23X, CR10(X),
21X, and CR7 Dataloggers ............................................................ 14
8. Example “2X32” Mode Program Loops for CR23X, CR10(X),
21X, and CR7 Dataloggers ............................................................ 15
9. Wiring Diagram for Strain Gages and Potentiometers............................. 16
10. Single-ended Measurement without Excitation...................................... 23
11. Differential Measurement without Excitation........................................ 23
12. Half Bridge (Modified 107 Temperature Probe) Hook-up and
Measurement.................................................................................. 24
13. Potentiometer Hook-up and Measurement............................................. 25
14. Four Wire Half Bridge Hook-up and Measurement............................... 26
15. Full Bridge Measurement....................................................................... 26
16. Full Bridge Measurement with Excitation Compensation ..................... 27
17. Differential Thermocouple Measurement with Reference
Junction at the Datalogger.............................................................. 29
18. Differential Thermocouple Measurement with Reference
Junction at the AM16/32................................................................ 29
19. AM16/32 Aluminum Cover Plate .......................................................... 30
20. Thermocouple and Soil Block Measurement......................................... 32
21. Mounting Tab Hole Pattern.................................................................... 35
iii
Cautionary Notes
The AM16/32 is not designed to multiplex power. Its intended function is to
switch low level analog signals. Switched currents in excess of 30 mA will
degrade the relay contacts involved, rendering that channel unsuitable for
further low level analog measurement. Customers who need to switch power
are directed to Campbell Scientific’s SDM-CD16AC, A6REL-12, or
A21REL-12 relays.
Changing the setting of the mode switch from “4X16” to “2X32” connects
COM ODD H to COM EVEN H and also COM ODD L to COM EVEN L.
After wiring AM16/32, exercise due care to avoid inadvertently putting excess
voltage on a line or short circuiting a power supply which might damage
datalogger, wiring panel, sensor or multiplexer (not covered under warranty).
This is a blank page.
1
AM16/32 Relay Analog Multiplexer
1. Function
The primary function of the AM16/32 Multiplexer is to increase the number of
sensors that can be measured by a CR1000, CR23X, CR10(X), 21X, or CR7
datalogger. The AM16/32 is positioned between the sensors and the
datalogger. The AM16/32 is a replacement for CSI’s AM416 and AM32
models. Mechanical relays in the AM16/32 connect each of the sensor
channels in turn to a common output destined for the datalogger. The user
program advances the multiplexer through the sensor channels making
measurements and storing data.
A slide switch located on the AM16/32’s top panel selects one of two modes of
operation. In “2X32” mode the multiplexer can scan 32 sensor input channels,
each with two lines. In “4X16” mode it can scan 16 input channels with four
lines a piece. The datalogger program is written according to the selected mode
and the sensors to be measured.
The maximum number of sensors that can be multiplexed by an AM16/32
depends primarily on the type(s) of sensors to be scanned. The following
guidelines assume identical sensors:
Up to 32 single-ended or differential analog sensors that do not require
excitation. For example: pyranometers and thermocouples (see Sections 6.1,
6.2, and 6.6).
Up to 32 single-ended sensors that require excitation. Example: some half
bridges (see Section 6.3.1).
Up to 16 single-ended or differential sensors that require excitation. Examples:
full bridges and four-wire half bridge with measured excitation (see Section
6.3.3 and 6.4).
In conjunction with a second AM16/32, up to 16 six-wire full bridges (Section
6.5).
1.1 Typical Applications
The AM16/32 is intended for use in applications where the number of required
sensors exceeds the number of datalogger input channels. Most commonly, the
AM16/32 is used to multiplex analog sensor signals, although it can also be
used to multiplex switched excitations, continuous analog outputs, or even
certain pulse counting measurements (i.e., those that require only intermittent
sampling). It is also possible to multiplex sensors of different, but compatible,
types (e.g., thermocouples and soil moisture blocks, see Section 6.7.1).
AM16/32 Relay Analog Multiplexer
2
For a discussion of single-ended versus differential analog
measurements, please consult the Measurement section of your
datalogger manual.
As purchased, the AM16/32 is intended for use in indoor, non-condensing
environments. An enclosure is required for field or high humidity use. In
applications where one or two multiplexers are deployed, the AM-ENC
(10” X 12”) enclosure is recommended.
1.2 Compatibility
The AM16/32 is compatible with Campbell’s CR5000, CR1000, CR23X,
CR10(X), 21X, and CR7 dataloggers.
The AM16/32 is compatible with a wide variety of commercially available
sensors. As long as relay contact current maximums are not exceeded (see
Cautionary Notes, page iii), and no more than four lines are switched at a time,
system compatibility for a specific sensor is determined by sensor-datalogger
compatibility.
In CR1000, CR23X, and CR10(X) applications the AM16/32 may be used to
multiplex up to 16 Geokon vibrating wire sensors through one AVW-1
vibrating wire interface.
2. Physical Description
The AM16/32 is housed in a 10.2 cm x 23.9 cm x 4.6 cm (4.0” x 9.4” x 1.8”)
anodized aluminum case (Figure 1). The aluminum case is intended to reduce
temperature gradients across the AM16/32’s terminal strips. An aluminum
cover plate is also included to this end. This is extremely important if
thermocouples are being multiplexed (Section 6.6).
The case can be opened for inspection/cleaning by removing two phillips-head
screws located on the under-side of the case. Mounting tabs are provided so
the AM16/32 can be fastened to a flat surface or an enclosure plate (Section 8).
All connections to the AM16/32 are made on the top panel terminal blocks.
The island of four terminals located near the mode switch are dedicated to the
connecting of datalogger power and control lines (Section 4.1). The four
“ODD” and “EVEN” “COM” terminals on the other side of the mode switch
carry shielded multiplexed sensor signals destined for datalogger analog inputs.
The remaining terminals on the AM16/32 are for sensor and sensor shield
connection (Section 4.2). The sensor inputs are not spark-gap protected. All
terminals accept stripped and tinned lead wires up to 16 AWG or 1.6 mm in
diameter. The datalogger-to-AM16/32 cabling requires a minimum of six and
as many as nine individually insulated wires with shields.
NOTE
AM16/32 Relay Analog Multiplexer
3
FIGURE 1. AM16/32 Relay Multiplexer
3. AM16/32 Specifications
Power*:Unregulated 12 VDC
Minimum Operating Voltage:
from –55C to +40C = 11.3 VDC;
from +40C to +85C = 11.8 VDC
(See Figure 2 for relay actuation times vs.
temperature and supply voltage.)
Current Drain: Quiescent: < 210 uA
Active: 6 mA typical in “2 x 32” mode
11 mA typical in “4 x 16” mode
Reset*:A continuous signal between 3.5 VDC and 16 VDC
holds the AM16/32 in an active state (where a clock
pulse can trigger a channel advance). A signal
voltage < 0.9VDC deactivates the AM16/32 (clock
pulse will not trigger a scan advance; AM16/32 is
also reset).
Clock*:On the transition from <1.5 V to >3.5 V, a scan
advance is actuated on the leading edge of the clock
signal; clock pulse should be a minimum of 1 ms
wide.
Operational
Temperature: Standard: -25oC to +50oC
Extended: -55oC to +85oC
Operational
Humidity: 0 - 95%, non-condensing
AM16/32 Relay Analog Multiplexer
4
Dimensions: Length – 23.9 cm (9.4")
Width - 10.2 cm (4.0")
Depth - 4.6 cm (1.8")
Weight: 1.5 lbs. (approx.), 693 g.
With AM ENC enclosure: 10.0 lbs., 4.54 kg
(approx.)
Mounting Tab
Hole Spacing: 1 inch x 3 inches x 9 inches. Up to 1/8 inch or 3 mm
diameter screws (see Figure 21).
Expandability**
(nominal): 4 AM16/32s per CR5000
4 AM16/32s per CR1000
4 AM16/32s per CR23X
4 AM16/32s per CR10(X)
4 AM16/32s per 21X
8 AM16/32s per CR7 725 Card
Maximum Cable
Length: Depends on sensor and scan rate. In general, longer
lead lengths necessitate longer measurement delays.
Refer to datalogger manual for details.
Maximum Switching
Current***:500 mA
Contact Specifications: Initial contact resistance: <0.1 ohm max.
Initial contact bounce: <1 ms
Contact material: Gold clad silver alloy
Wiper to N.O. contact capacitance: 0.5 pF
Typical low-current (<30 mA) life: 5 x 107
operations
Relay Switching Thermal emf: 0.3 uV typical; 0.5 uV maximum
Characteristics
(applying 11.3 – 14
VDC):
Operate time: <10 ms over temperature and supply
ranges
Break before make guaranteed by design
*Reset, Clock, and +12V inputs are protected by +16V transzorbs.
** Assumes sequential activation of multiplexers and that each datalogger channel is uniquely
dedicated. If your application requires additional multiplexing capability, please consult CSI for
application assistance.
*** Switching currents greater than 30 mA (occasional 50 mA current is acceptable) will degrade
the contact surfaces of the mechanical relays (increase their resistance). This will adversely affect
the suitability of these relays to multiplex low voltage signals. Although a relay used in this
manner no longer qualifies for low voltage measurement, it continues to be useful for switching
currents in excess of 30 mA.
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