Sensoray 618 - Manual (Page 5)

Sensoray Model 618/619 Smart A/D 3 Configuration
3 Configuration
The Smart A/D board requires the configuration of
programming shunts to select hardware options. These
options must be configured before installing the Smart
A/D board into the target system. Shunts are configured
by installing or removing shorting shunt plugs, at various
locations on the Smart A/D circuit board, as appropriate
for your application.
A supply of programming shunts, of sufficient number to
program all board options, is included with the Smart
A/D board.
3.1 Signal Conditioning Circuit (SCC)
Each channel is provided with a signal conditioning
circuit (SCC) which may be inserted into the sense signal
path. This conditioning circuit performs three functions:
• Common-mode tie-down. This function helps to
prevent the common mode voltage (CMV) from
straying beyond the input CMV range of the Smart
A/D measurement section. This function is required
when a sensor channel is driven from an isolated
source, such as a battery, isolated power supply, or
thermocouple.
• Open-sensor detect. If either of the two sense signals
should become disconnected from the source, this
function forces a differential voltage of 700mV,
minimum, to appear across the sense inputs. This
function is useful when a sensor is used in a control
loop.
• RF shunt. This function, which shunts RF noise to
ground, is essential when connecting to isolated
sources, such as thermocouples.
3.1.1 Side Effects
Sense input impedance is reduced when a channel’s SCC
is enabled. See “General Specifications” on page 19 for
details.
3.1.2 Recommended Settings
The decision of whether or not to enable a channel SCC
is influenced primarily by the type of sensor to be
interfaced, and, in the case of active sources, whether or
not the source is ground-referenced.
Listed below are recommendations for enabling vs.
disabling the SCC:
3.2 Shunt Mapping
Shunts E1 through E32 are used to control the enabling
of SCCs for all sensor channels. Each channel is
affiliated with two shunts. To enable a channel’s SCC,
you must install both of the affiliated shunts. Similarly,
to disable the SCC, you must remove both shunts.
The following tables show the mapping between
channels and affiliated shunt pairs for SCC enables.
For example, install shunts E3 and E19 to enable the
SCC for sensor channel 2.
Table 1: Recommended signal conditioner settings
Sensor Type SCC
Ungrounded Thermocouple Enabled
Isolated DC Voltage Source
Grounded Thermocouple Disabled
Ground-referenced DC Voltage Source
4-to-20 mA loop
Resistor
RTD
Strain/Pressure Gage
Thermistor
Table 2: Signal Conditioner shunt mapping, channels 0-7
Channel 0 1 2 3 4 5 6 7
Shunt
Numbers
E1 E2 E3 E4 E5 E6 E7 E8
E17 E18 E19 E20 E21 E22 E23 E24
Table 3: Signal Conditioner shunt mapping, channels 8-15
Channel 8 9 10 11 12 13 14 15
Shunt
Numbers
E9 E10 E11 E12 E13 E14 E15 E16
E25 E26 E27 E28 E29 E30 E31 E32