Novatech Bitronics M87X Series, Manual

Page: 137 / 184

ML0021 August 15, 2018
121
Copyright 2018 Bitronics, LLC
The I/O Board contains the analog input and isolation circuitry, output relay and drive
circuitry, as well as input protection and EMI/RFI suppression.
9.7.2 P31
The P31 Digital I/O Module consists of four circuit boards, the CompactPCI
TM
Interface
Board (692), the LED Daughterboard (717), and two I/O Boards (693 supports pins 1-16,
and 716 for pins 17-32). The Interface Board assembly contains the CompactPCI
TM
backplane connector and interface circuitry, front panel LEDs, and jumper blocks for output
relay power-up configuration.
The I/O Boards (693 and 716) contain the analog input and isolation circuitry, input
protection and EMI/RFI suppression, as well as output relay and drive circuitry (693 only).
9.7.3 P33
The P33 Digital Output Module consists of two circuit boards, the main board (803)
contains the CompactPCI
TM
Interface and all of the output circuitry. Moveable jumpers are
located on this board that are used to set each relay output as either normally open (NO)
or normally closed (NC). Daughterboard (803A) consists of the LED’s used to indicate the
relay status. An LED is turned on when its respective relay coil is energized.
9.8 System Design Considerations
9.8.1 Input / Output Impedance
On the P30A and P31, all of the output relay terminals are shared with the circuitry for a
digital input. As a result, there is always an impedance across the output relay contacts,
even when the relay is not energized. The value of the impedance depends on the
configuration of the input, or more specifically, the setting for the input threshold. The input
circuitry is shown in Figure 11 (pg.112).
THIS PARALLEL IMPEDANCE WILL CAUSE A
CURRENT TO FLOW THROUGH ANY LOADS THAT ARE CONTROLLED BY THE
RELAY WHEN THE RELAY CONTACTS ARE OPEN.
IT IS IMPORTANT TO
CONSIDER THIS CURRENT WHEN SELECTING THE INPUT THRESHOLD, AND
WHEN DESIGNING SYSTEMS USING THE OUTPUT RELAYS.
If the input is set for a low threshold (15V), then the impedance across the relay terminals
is 33k
Ω . On a 125Vdc system, this equates to a maximum of 3.8mA, depending on the
impedance of any loads in the loop. If the input is set for a high threshold (70V), then the
impedance across the relay terminals is 153k
Ω . On a 125Vdc system, this equates to a
maximum of 817 μ A , depending on the impedance of any loads in the loop.
9.8.2 Input Assignments
Due to the shared nature of some of the I/O circuitry, careful planning should be used in
assigning the inputs and outputs of the P30A/P31 module. The user is reminded that the
first four inputs on either module are shared with the four outputs.
SERIOUS SYSTEM
AND/OR PRODUCT DAMAGE COULD RESULT FROM HAVING AN OUTPUT RELAY
OPERATE WHILE CONNECTED TO AN INPUT.
For this reason, it is recommended that
the user assign inputs 5-8 (those not shared with inputs) prior to using the first four inputs.