Impulse SCMPB01 - Manual (Page 6)

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Isolated Analog Signal Conditioning Products SCM5B
SCM5B
Ordering Information
Part Number Description
SCMPB02 Standard 16-channel backpanel.
SCMPB02-1 SCMPB02 without cold junction compensation circuits. Use
when cost savings is desired and thermocouple input modules
SCM5B37 snd SCM5B47 will not be used.
SCMPB02-2 SCMPB02 with DIN rail mounting option. The backpanel
is mounted on a piece of anodized aluminum, which is captured
by the SCMXBEFE DIN rail mounting elements. The backpanel
is shipped fully assembled.
SCMPB02-3 SCMPB02-1 with DIN rail mounting option. See SCMPB02
and SCMPB02-2 for details.
Electrical
P1 Connector
The 26 pin P1 connector provides the signal interface between the SCMPB02
backpanel and the host measurement system. Two separate analog bus
connections are provided; one for analog input signals and one for analog output
signals. Two sets of six address lines and an enable pin allow input and output
modules to be independently multiplexed onto their respective analog signal
bus. R0 thru R5 and RD EN\ are used for input modules, and W0 thru W5 and
WR EN\ are used for output modules.
Address Selection
The SCMPB02 backpanel has address decoding circuitry to allow multiplexing
any combination of up to 16 input or output modules. Capability is also provided
in the address decode circuitry to expand the system to 64 channels (four
SCMPB02 backpanels) of multiplexed input or output. Jumpers on HD10
header, E1 and E2 group, select which set of 16 addresses are assigned to a
particular backpanel. The E1 group assigns a set of 16 addresses for input
modules, and the E2 group assigns a set of 16 addresses for output modules.
The table below shows the correlation of jumper position to address range.
E1 Jumper Pos E2 Jumper Pos Address Range/Mode
4 4 0-15, STAND ALONE
3 3 48-63, EXPANDED
2 2 32-47, EXPANDED
1 1 16-31, EXPANDED
0 0 0-15, EXPANDED
To connect multiple SCMPB02 backpanels in this expanded configuration, use
interconnect cable SCMXCA004-XX.
Power
The SCMPB02 backpanel requires external +5VDC ±5% power. The chassis
mounted SCMXPRE-003 or SCMXPRT-003 power supplies have adequate
capacity to power any combination of modules.
Fusing
The SCMPB02 backpanel power is fuse protected through F1. This is a Littlefuse
type 252007, 7 amp fuse. Zener diode DZ1 provides extra protection by
clamping the input power voltage to +5.6V. If the input supply voltage connection
is reversed, this zener diode will be forward biased and fuse F1 will be blown.
Grounding
Figure 7 below details the optional ground jumper configuration available on
the SCMPB02 backpanel. Jumpers J1, J2, and J4 are factory installed.
Jumper J1 connects the SIG COM shield wires (pins 2, 5, and 6) to the backpanel
signal ground. This provides a ground connection between the host system and
backpanel. Jumper J1 is required if output modules (SCM5B39, SCM5B49) are
used, or if there is no high impedance sense input (input low of a differential or
pseudo-differential system) on the host measurement system.
Jumper J2 connects the SNS LO line (pin 4) to the backpanel signal ground.
If the host system has the capability, this allows measuring the SCMPB02
ground potential.
For proper operation of the output switch or track-and-hold circuit when using
the SCMPB02/06 backpanels, a current path must exist between the host
control logic power common and module I/O Common (module pin 19). This
path can be established on the SCMPB02 via jumper J4. If this connection exists
elsewhere in the system, jumper J4 should be removed since possible ground
loops could exist. Other connections of power ground and signal ground usually
occur at the A/D or D/A converter of the host measurement system. More
information on grounding can be found in Application Note AN502.
If the connection of power common and SIG COM shield wires exist in the host
measurement system, a resistive connection between SIG COM and the
backpanel signal ground can be made via R
1
. R
1
can be as large as 10K ohms;
100 ohms is a recommended value. Jumper J3 can be used to connect the SNS
LO line to R
1
when this ground configuration is used.
For full protection against large electrical disturbances on the field-side of the
SCM5B modules, a #10-32 ground stud is provided on the backpanel. An
electrical connection between this ground stud and system ground should be
provided with a large gauge wire of the shortest possible length. When this
connection is made, a possible ground loop could result through the SIG COM
shield wires and backpanel signal ground. If the application involves only input
modules and a differential input is used by the host measurement system, J1
should be removed. Remember that J1 is required if output modules are used
or if the host system does not have differential inputs.
Figure 7: SCMPB02 Grounding Diagram