Connections, Overview, Termination boards – Sensoray 118 User Manual

Page 8: Sensor hot insertion, Connector pinout, Reference junction sensor, Sensor channels, Sense terminals, Excitation terminals, Shield terminal

Sensoray Model 118 Smart A/D™ Instruction Manual

Connections

4 Connections

4.1 Overview

Sensors are connected to the Smart A/D™ by means of
40-pin header P1, located at the edge of the circuit board
as shown in Figure 2.

4.1.1 Termination Boards

It is recommended that sensors be indirectly connected to
the Smart A/D™ board by means of an optional screw
termination board (TB), such as Sensoray models
7409TB or 7409TC. These TBs have calibrated
reference sensors for thermocouple compensation and are
designed to mate directly to all Smart A/D™ boards.

4.1.2 Sensor Hot Insertion

Sensors may be electrically connected and disconnected
from the Smart A/D™ or termination board without
removing the Smart A/D™ board or power from the
backplane.

4.2 Connector Pinout

The pinout of header P1 is shown in Figure 4.

Figure 4: Header P1 pinout

4.2.1 Reference Junction Sensor

Three of the signals—+12V, GND and TREF— shown at
the bottom of connector P1 are used for interfacing the
Smart A/D™ to a remote thermocouple

reference-junction temperature sensor. One such sensor
is provided on all models of Sensoray Smart A/D™
termination boards.

The +12V and GND signals provide excitation to the
reference sensor. The TREF connection provides a path
from the sensor output to a dedicated input channel on
the Smart A/D™ board.

If you are using thermocouples in your application and
you will be implementing your own termination system,
you must provide your own remote temperature sensor.
The sensor, which produces an output of 10mV/°K, must
have its output signal routed to the TREF pin.

4.3 Sensor Channels

Each sensor channel provides five signals for interfacing
to a sensor. A sensor can have as many as five
connections to a channel or as few as two.

4.3.1 Sense Terminals

Two of the channel signals, designated V+ and V-, are
universally used for all sensor types. These two signals
are, respectively, the positive and negative differential
voltage sense inputs.

Since the sense inputs accept differential signals, it is not
required for either of the two input signals to be at ground
potential. The Smart A/D™ digitizer measures only the
difference voltage across the two sense inputs.

Due to common-mode voltage (CMV) input constraints,
however, you must ensure that neither sense input, with
respect to system ground, exceeds the maximum input
CMV permitted by the Smart A/D™.

Small excursions beyond the CMV limit may degrade
measurement accuracy on the offending channel, while
large excursions may cause measurement errors on other
sensor channels, or worse yet, damage the board.

See “Sensor Specifications” on page 36 for input CMV
limit values.

4.3.2 Excitation Terminals

Passive sensors require connection to the I+ and I-
signals. The I+ and I- signals supply positive and
negative excitation, respectively, to passive sensors.

V+

V-

Ch0

I+

I-

Ch0

V+

V-

Ch1

I+

I-

Ch1

V+

V-

Ch2

I+

I-

Ch2

V+

V-

Ch3

I+

I-

Ch3

V+

V-

Ch4

I+

I-

Ch4

V+

V-

Ch5

I+

I-

Ch5

V+

V-

Ch6

I+

I-

Ch6

V+

V-

Ch7

I+

I-

Ch7

GND

N.C.

TREF

SHIELD

+12V

GND

SHIELD

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