P31; P33; System Design Considerations; Input / Output Impedance - Novatech Bitronics M87X Series Manual

Table of Contents

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

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

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).

The P33 Digital Output Module consists of two circuit boards, the main board (803)

contains the CompactPCI

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.

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 33kΩ. 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 153kΩ. On a 125Vdc system, this equates to a

maximum of 817μA, depending on the impedance of any loads in the loop.

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.

121

ML0021

August 15, 2018

Table of Contents