Campbell Scientific AM25T 25-Channel Solid State Multiplexer - Manual (Page 8)

AM25T Solid State Multiplexer
Ground (GND)
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 (
). Always tie the
datalogger and multiplexer to a common earth ground via the grounding lug.
Analog Ground (AG)
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 (
). Terminal AG must be connected to
datalogger ground as shown in Table 3-1.
Reset (RES)
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.
Clock (CLK)
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. NOTE
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.
2. Installation
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.
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.
4