Table of Contents
Advertisement
SD39EAM-1r4
R1 prevents excessive current into the ASIC when a signal up to 30 Vdc (or a miswiring up to 120 Vac) is
applied to the VIN terminal. In addition, in the event of a fault within the ASIC, R1 prevents large
currents from being supplied to field wiring.
4.2.1.2 Current Inputs
Current input connections are made to the PWR and COM terminals. For 2-wire (4-20 mA) current
inputs, power is supplied through Opto-Coupler Q1 (which is saturated on) to the PWR terminal. The
return is through Q2, which is turned on hard, and current sense resistor R3. R3 converts the current to a
voltage, which is read by the ASIC at its I-Sense input through resistor R2.
The voltage input to I-Sense is an input to an internal ADC and pulse counting and timing circuits. In
analog current input mode, the resistor R2 is internally connected to the external capacitor C1 on the C-
Alias pin of the ASIC. This forms an anti-alias RC low-pass filter for the ADC.
4.2.1.3 Current Outputs
Current output connections are made to the PWR and COM terminals. Power is supplied through Opto-
Coupler Q1 - which is saturated on - to the PWR terminal. The return is through Q2 and current sense
resistor R3. However, in this case, Q2 is not turned on hard. Q2 is controlled by a feedback circuit
within the ASIC so that current sensed by R3 and the I-Sense input agrees with the desired output current.
4.3
EAM Redundancy
EAM redundancy is accomplished by rack-to-rack type redundancy through pairs of duplicate racks of
I/O and control modules that share a common I/O termination such as the EAM Marshalled Termination
Assembly.
The EAM in standby mode is identified by a solid Green "OK" LED and a Black (OFF) ACTIVE LED.
If the controller in the active rack detects an error in a module within its rack, it will transfer control to the
controller in the redundant rack. The redundant controller will then enable all the I/O modules under its
control. A solid Green ACTIVE LED indicates an enabled module.
4.4
EAM Diagnostics
Part of the EAM program includes the execution of diagnostics that can detect the following types of field
and hardware errors.
Field Problems
•
Open Circuit
•
Short Circuit
•
Under-Range
•
Over-Range
September 2005
Circuit Description
4-5
Advertisement
Table of Contents
