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AM25T Solid-State Thermocouple Multiplexer
2
2. Precautions
•
The AM25T is not designed to multiplex power. Its intended function is to
switch low-level analog signals. Switched currents in excess of 25 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.
•
After wiring an AM25T, exercise due care to avoid inadvertently putting
excess voltage on a line or short circuiting a power supply which might
damage connected devices such as data logger, wiring panel, sensor, or
multiplexer (not covered under warranty).
3. Initial Inspection
•
The AM25T ships with:
o
AM25T Cover
o
Mounting Grommet (qty: 4)
o
Mounting Screw (qty: 4)
•
Upon receipt of the AM25T, inspect the packaging and contents for
damage. File damage claims with the shipping company.
•
Immediately check package contents. Thoroughly check all packaging
material for product that may be concealed. Check model number, part
numbers, and product descriptions against the shipping documents. Model
or part numbers are found on each product. On cables, the number is often
found at the end of the cable that connects to the measurement device.
Ensure that the expected lengths of cables were received. Contact
Campbell Scientific immediately if there are any discrepancies.
4. Overview
The AM25T is connected to the data logger 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 data logger.
4.1 Measurement Terminals
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
.
4.2 Excitation Terminal (VX)
This terminal is used to excite the reference temperature (PRT) on the AM25T.
The excitation line is protected from transients with a transorb. (Earlier
versions of the AM25T, prior to serial number 1839, used a Zener diode for
protection. The diode limited the negative excitation voltage to –400 mV.)