Campbell Scientific AM25T User Manual
AM25T Solid State Multiplexer
Revision: 1/10
Copyright © 1995-2010
Campbell Scientific, Inc.
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. A
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AM25T Solid State Multiplexer
Table of Contents
PDF viewers note: These page numbers refer to the printed version of this document. Use
the Adobe Acrobat® bookmarks tab for links to specific sections.
1. General .........................................................................1
1.1 AM25T Specifications..............................................................................1
1.2 Physical Description.................................................................................2
1.3 Operation..................................................................................................3
2. Installation....................................................................4
3. Datalogger to AM25T Wiring.......................................5
4. Sensor to AM25T Wiring .............................................6
4.1 Thermocouple Measurement....................................................................6
4.2 Differential Analog Measurements...........................................................7
4.3 Mixed Sensor Types.................................................................................7
5. General Measurement Considerations......................8
6. Datalogger Programming............................................8
6.1 CRBasic Programming.............................................................................8
6.1.1 Example CRBasic Programs.........................................................11
6.1.1.1 CR1000 Example Program 1...............................................11
6.1.1.2 CR1000 Example Program 2...............................................12
6.2 Edlog Programming................................................................................ 13
6.2.1 Example CR10(X) Programs........................................................14
6.2.2 Example CR23X Program ............................................................18
Appendices
A. Single-Ended Measurements.................................A-1
A.1 Directions for Single-Ended Measurements....................................... A-1
A.2 Indexing with Loops........................................................................... A-5
B. Differences Between the AM25T, AM416, and
the AM32........................................................................B-1
i
AM25T Solid State Multiplexer Table of Contents
Figures
1. AM25T Thermocouple Multiplexer........................................................... 3
2. External Battery Connections .................................................................... 6
3. Differential Measurement of Type T Thermocouple................................. 7
4. Differential Voltage Measurement............................................................. 7
A-1. Single-Ended Measurement of a Type T Thermocouple...................A-2
A-2. Single-Ended Measurement...............................................................A-5
Tables
3-1. Datalogger to AM25T Wiring................................................................ 5
6-1. Wiring for CR1000 Example 1............................................................. 11
6-2. Wiring for CR1000 Example 2............................................................. 12
6-3. RTD Excitation Voltage and Measurement Range for AM25T
Multiplexers Prior to Serial Number 1839........................................ 14
6-4. Wiring for CR10(X) Examples............................................................. 14
6-5. Wiring for CR23X Example................................................................. 18
A-1. Values in Input Storage; Input Location Not Indexed.......................A-5
A-2. Values in Input Storage; with Input Location Index and without
Step Loop Index Instruction............................................................A-6
A-3. Values in Input Storage; with Input Location Index and Step
Loop Index Instruction....................................................................A-6
Program Examples
1. CR1000 Program Using One Instruction to Measure Both the
Reference Temperature and Thermocouples.....................................11
2. CR1000 Program that Uses Separate AM25T Instructions to
Measure the PRT and Thermocouples .............................................. 12
3. CR10(X) Program for Measuring 25 Type T Thermocouples or
Voltage Sensors Using a Differential Instruction.............................. 14
4. CR10(X) Program for Measuring 25 Type T Thermocouples with
the Differential Thermocouple Instruction and Long Lead
Length Compensation on the RTD Measurement............................. 16
5. CR23X Program for Measuring 25 Type T Thermocouples.................... 18
A-1. CR10 Program for Measuring 50 Type T Thermocouples or
Voltage Sensors Using a Single-Ended Instruction.........................A-2
A-2. 21X Program for Measuring 50 Type T Thermocouples or
Voltage Sensors Using Single-Ended Instruction ..........................A-3
A-3. Single-Ended Thermocouples, Input Location Not Indexed .............A-6
A-4. Measuring Single-Ended Thermocouples with the Input
Location Indexed and no Step Loop Index .....................................A-7
A-5. Measuring Single-Ended Thermocouples with the Input
Location Indexed and Step Loop Index .........................................A-7
ii
AM25T Solid State Multiplexer
1. General
The AM25T Multiplexer increases the number of channels for measuring
thermocouples or voltage sensors with Campbell Scientific dataloggers. The
AM25T is positioned between the sensors and the datalogger. The datalogger
controls the AM25T's solid state relays, sequentially connecting each sensor to
the datalogger.
The AM25T is not suitable for resistive bridge measurements (high impedance
of the solid state relays) or multiplexing power (25 mA maximum switching
current).
A maximum of 25 thermocouples (differential voltage measurement) can be
multiplexed by an AM25T. Single-ended voltage measurements are not
recommended (Appendix A).
The AM25T must be used in a non-condensing environment. An enclosure is
required for field use. In applications where one or two multiplexers are
deployed in the field, the ENC12/14 can be used. The ENC16/18 can be used
to house several multiplexers at the same site.
1.1 AM25T Specifications
POWER
Unregulated 9.6 V to 16 V; 12 VDC Nominal
CURRENT DRAIN
Quiescent: 0.5 mA
Active: 1.0 mA (typical)
ENABLE
Inactive: < 0.9 V
Active: 3.5 to 5.0 V (7 V max.)
CLOCK
The relays are advanced on the falling edge of the clock pulse (transition from
>3.5 V to <1.5 V; 7 V max.). The minimum clock pulse width is limited by
the datalogger.
Minimum ON time 50 microseconds
Minimum OFF time 60 microseconds
1
AM25T Solid State Multiplexer
OPERATING TEMPERATURE
Standard: -40°C to +85°C
RTD accuracy ±0.4°C
OPERATING HUMIDITY
Noncondensing: 0 to 95%
DIMENSIONS
Length: 23.6 cm (9.3”)
Width: 5.10 cm (2.0")
Depth: 13.2 cm (5.2”)
WEIGHT
0.91 kg (2.0 lbs)
3.6 kg (8.0 lbs); Shipping
EXPANDABILITY (nominal)**
2 AM25Ts per CR800 or CR850
4 AM25Ts per CR1000
6 AM25Ts per CR23X
4 AM25Ts per CR10(X)
6 AM25Ts per 21X
7 AM25Ts per CR7 725 Card
MAXIMUM CABLE LENGTH
Multiplexers can be located up to 305 m (1000 ft) from the datalogger. When
lightning protection is required, do not exceed 152 m (500 ft) in cable length. The
spark gaps will not fire if the heavy ground wire is longer than 152 m (500 ft).
TYPICAL RELAY RESISTANCE
500 Ω
MAXIMUM SWITCHING CURRENT
25 mA; Switching currents greater than 25 mA will damage the relays and render
them unusable.
**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.
1.2 Physical Description
The AM25T is housed in an anodized aluminum case with a cover that will
help reduce temperature gradients across the AM25T's terminal strips
(Figure 1).
2
AM25T
SOLID STATE THERMOCOUPLE
MULTIPLEXER
MADE IN USA
S / N
AM25T
SOLID STATE THERMOCOUPLE
MULTIPLEXER
LOGAN UTAH
Logan, Utah
AM25T Solid State Multiplexer
The terminal strips that run the length of the AM25T are for sensor
connections. All inputs are protected by spark gaps. All terminals accept
stripped and tinned lead wires up to 1.5 mm (0.059 inches) in diameter. A
strain-relief flange is located between the input terminals.
SOLID STATE THERMOCOUPLE
AM25T
MULTIPLEXER
MADE IN USA
RES
EX
CLK
13L
12L
12H
1H
HI
LO
AG
14H 14L13H
2H2L3H3L4H 4L 5H
1L+12
Logan, Utah
15H
16H 16L
15L
17H
18H
17L
FIGURE 1. AM25T Thermocouple Multiplexer
1.3 Operation
Measurement Terminals
Excitation Terminal
9L
AM25T
18L
19H 19L
5L
6H
SOLID STATE THERMOCOUPLE
MULTIPLEXER
20H 20L
8H
7L
6L
7H
MADE IN USA
21L
22H
21H
10H
11H
10L
9H
8L
23H
23L
22L
11L
S / N
1011
25H 25L
24L
24H
The AM25T is connected to the datalogger with eight insulated wires and a
large ground wire. These wires are used to power and control the multiplexer,
and connect the common analog inputs to the datalogger.
There are 25 differential channels on the AM25T. These channels are labeled
1H and 1L through 25H and 25L. The channels are sequentially connected and
reversed to the common channels HI and LO.
This terminal is used to excite the reference temperature (RTD) on the
AM25T. The excitation line is protected from transients with a transorb.
(Earlier versions of the AM25T, prior to 1839, used a zener diode for
protection. The diode limited the negative excitation voltage to -400 mV).
Power (12 V)
The AM25T requires a 9.6 to 16 VDC (12 VDC nominal) power supply.
In low current drain applications, it is convenient to power the AM25T from
the datalogger's battery. For power intensive operations, use a high Amp hour
12 VDC battery.
See Campbell Scientific’s application note on power supplies for information
on calculating the power requirements of your system.
3
AM25T Solid State Multiplexer
Ground (GND)
Analog Ground (AG)
Reset (RES)
Each differential input channel has a ground terminal located next to it. The
ground terminal is common with the power ground and the ground lug on the
base. Connect the sensor shields to the ground terminals (
datalogger and multiplexer to a common earth ground via the grounding lug.
The analog ground (AG) terminal is the ground reference for the AM25T
reference temperature measurement. AG ground is not common with the other
ground terminals labeled (
datalogger ground as shown in Table 3-1.
A control port is used to operate the RES channel. The AM25T is reset and
activated by applying and holding 5 VDC to the RES channel. Once the
AM25T is activated, the AM25T reference temperature can be immediately
measured. The AM25T enters its quiescent state when the RES channel is set
to 0 VDC.
). Terminal AG must be connected to
). Always tie the
Clock (CLK)
NOTE
2. Installation
Pulsing the CLK channel sequentially advances the relays. A control port is
used to operate the CLK channel.
The first CLK pulse advances the relays to the reference temperature excitation
channel. The second CLK pulse advances the relays and connects HI and LO to
1H and 1L on the multiplexer.
Two clock pulses are required to advance to the next adjacent
sensor input channel on the AM25T.
The fourth CLK pulse advances the relays and connects HI and LO to 2H and
2L. The sixth CLK pulse advance the relays and connects HI and LO to 3H
and 3L. This sequence is continued for the remaining input channels.
The standard AM25T may be operated in a non-condensing environment. An
enclosure is required for field use.
Campbell Scientific’s ENC12/14 and ENC16/18 enclosures offer a degree of
protection against dust, spraying water, oil, falling dirt, or dripping non-corrosive
liquids. The enclosures contain plates for multiplexer mounting and conduit
bushings for cable entry. These enclosures are rain tight but not waterproof.
4
The enclosure lids have water resistant gaskets. Electricians putty is shipped
with the enclosures to seal around the cable entry to reduce the moisture
entering the enclosure. Desiccant should be kept in the enclosure and
exchanged regularly or as indicated by the humidity indicator.
U-bolts are used to attach the enclosures to a 1.25" NPT pipe. The enclosure
may also be lag-bolted to a wall or similar flat surface.
Fasten the AM25T to the enclosure backplate. Securely fasten the leads to the
strain relief flange running between the AM25T terminal strips and install the
cover to reduce temperature gradients during thermocouple measurements.
3. Datalogger to AM25T Wiring
When powering the AM25T from the same battery as the datalogger, connect
the datalogger to the AM25T as shown in Table 3-1. Two CABLE4CBL-L
cables typically carry control, power, and measurement signals between the
AM25T and the datalogger.
AM25T Solid State Multiplexer
WARNING
Caution
Function
+12V Power 12 V 12 V 12 V 12 V 12 V
Power and Shield Ground
Clock CLK Control Port Control Port Control Port Control Port
Reset RES Control Port Control Port Control Port Control Port
RTD Excitation EX Excitation Excitation Excitation Excitation
Analog Ground AG AG
Common High HI Diff. Chan. H Diff. Chan. H Diff. Chan. H Diff. Chan. H
Common Low LO Diff. Chan. L Diff. Chan. L Diff. Chan. L Diff. Chan. L
Do not reverse the polarity of the +12 Volt and Ground
leads. Damage to the multiplexer, sensors, and
datalogger will occur.
A separate battery can be used to power the AM25T. A separate battery might
be used when the AM25T is installed some distance from the datalogger.
Ground must be connected between the datalogger and the AM25T (Figure 2).
When leads in excess of 152 m (500 feet) are used to connect the datalogger to
the AM25T, it may be necessary to compensate for the drop in RTD excitation
voltage (program example 4).
All AM25T inputs are spark gap protected. To ensure that
the spark gaps fire, the large ground wire between the
AM25T and datalogger must not be greater than 152 m
(500 ft). In applications where lightning protection is not
required, limit the cable length between the AM25T and
datalogger to 305 m (1000 ft).
TABLE 3-1. Datalogger to AM25T Wiring
AM25T
CR10(X)
G
21X/CR7
CR23X
G G
CR800,
CR850,
CR1000,
CR3000,
CR5000,
CR9000X
5
AM25T Solid State Multiplexer
FIGURE 2. External Battery Connections
4. Sensor to AM25T Wiring
This section and the examples describe differential voltage measurements of
thermocouples. It is possible to make single-ended measurements with the
AM25T, however they are more likely to have problems (Appendix A).
Shield wires are connected to the ground terminal next to the measurement
channel and left unattached at the sensor.
AM25T
4.1 Thermocouple Measurement
An internal reference RTD is located in the AM25T. This reference
temperature does not require an additional datalogger input to measure the
reference. The RTD is located in the center of the multiplexer on the strain
relief flange.
Thermal gradients between the AM25T's sensor input terminals and the RTD
cause errors in thermocouple readings. For example, a one degree gradient
between input terminals and the RTD will result in a one degree measurement
error. The central aluminum (strain relief) bar and the cover are designed to
reduce gradients.
Heat conduction along the thermocouple wire, into the terminal strips, can be
reduced by coiling some excess lead wire inside the enclosure.
The datalogger manual contains a thorough discussion on thermocouple
measurements and error analysis. Consult the datalogger manual for more
details.
For a differential voltage measurement of a thermocouple, wire the high side of
the thermocouple to the high side of a differential input channel and the low
side of the thermocouple to the low side of the channel. Thermocouples that
follow the U.S. industry standards use red insulation on the low side of the
thermocouple. Wire one thermocouple per differential input channel
(Figure 3).
6
FIGURE 3. Differential Measurement of Type T Thermocouple
4.2 Differential Analog Measurements
Connect one differential sensor to a differential AM25T input channel.
Connect the sensor shields to the ground terminals next to the input channel.
Up to 25 differential sensors may be measured by one differential channel on
the datalogger (Figure 4).
AM25T Solid State Multiplexer
4.3 Mixed Sensor Types
Different sensors may be mixed on the AM25T. Additional loops and
measurement instructions will be required.
FIGURE 4. Differential Voltage Measurement
7
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