Campbell AM416, Instruction Manual

1

AM416 RELAY MULTIPLEXER

1.  FUNCTION

The primary function of the AM416 Multiplexer
is to increase the number of sensors that may
be scanned by Campbell's CR10(X), 21X and
CR7 dataloggers.  The AM416 is positioned
between the sensors and the datalogger;
mechanical relays are used to switch the
desired sensor signal(s) through the system.
Most commonly, users will multiplex signals
from analog sensors into single-ended or
differential datalogger channels.  Four lines are
switched simultaneously; a maximum of sixteen
sets of (four) lines may be scanned, hence the
name 

A

(nalog) 

M

(ultiplexer) 

4

(lines x) 

16

(sets).

Therefore, a total of 64 lines may be
multiplexed.

The maximum number of sensors that can be
multiplexed through one AM416 depends
primarily upon the type(s) of sensors to be
scanned.  Some examples (assuming identical
sensors) follow:

1.  Up to 32 single-ended or differential

sensors that do not require excitation (e.g.
pyranometers, thermocouples; Sections
6.1, 6.2, and 6.6).

2.  Up to 48 single-ended sensors that require

excitation (e.g. some half bridges; Section
6.3.1).

3.  Up to 16 single-ended or differential

sensors that require excitation (e.g. full
bridges, four-wire half bridge with measured
excitation; Section 6.3.3 and 6.4).

4.  In conjunction with an AM32 multiplexer, up

to 16 six-wire full bridges (Section 6.5).

1.1.  TYPICAL APPLICATIONS

The AM416 is intended for use in applications
where the number of required sensors exceeds
the number of datalogger input channels.  Most
commonly, the AM416 is used to multiplex
analog sensor signals, although it also may 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 6.6).

NOTE:

  For a discussion of single-ended

versus differential analog measurements,
please consult the Measurement Section of
your datalogger manual.

As purchased, the AM416 is intended for use in
indoor, non-condensing environments.  An
enclosure is required for field use.  In non-
thermocouple applications where a single
multiplexer is deployed, the AM-ENC enclosure
is recommended.  In thermocouple applications,
CSI recommends use of the AM-ENCT
enclosure.  If several multiplexers are deployed
at the same site in a non-thermocouple
application, the 024 or 030 enclosures provide
cost-effective housing options.

1.2  COMPATIBILITY

The AM416 is compatible with Campbell's
CR10(X), 21X or CR7 dataloggers.

The AM416 is compatible with a wide variety of
commercially available sensors.  As long as
current limitations are not exceeded, and no
more than four lines are switched at a time,
system compatibility for a specific sensor is
determined by sensor-datalogger compatibility.

In CR10(X) applications, the AM416 may be
used to multiplex up to 16 Geokon vibrating wire
sensors through one AVW-1 vibrating wire
interface.

2.  PHYSICAL DESCRIPTION

The AM416 is housed in a 21 cm x 16.5 cm x
3.5 cm (8.2" x 6.5" x 1.5") anodized aluminum
case (Figure 1).  The aluminum case is
intended to reduce temperature gradients
across the AM416's terminal strips.  This is
extremely important when thermocouples are
being multiplexed (Section 6.6). The case may
be opened by removing the four #1 phillips-
head screws located at the corners of the case.
Disassembly of the case may be required to
mount the AM416 to a plate or an enclosure
(Section 8).

A strain-relief flange is located along the lower
edge of the top panel of the case.  Several
plastic wire ties are included with the AM416 to
attach wires to this flange.