Field Connections; 4.2.1.1 Voltage Inputs - Siemens APACS+ Installation And Service Instruction

Circuit Description
4.2.1

Field Connections

The EAM Termination Strip and EAM Marshalled Termination Assembly each provide isolated
termination for 16 channels of I/O. A channel comprises 4 terminals:
•
PWR - Field Power Source
•
VIN - Field Signal (Analog/Discrete Voltage Input)
•
COM - Field Signal Common (Return)
•
SHLD - Cable Shield
There are three basic types of field terminal connections: voltage input, current input, and current output.

4.2.1.1 Voltage Inputs

Analog voltage input connections are made to the VIN and COM terminals. The COM connection is
completed through the N-Channel FET Q2, which is turned on hard, and the current sense resistor R3.
The voltage signal at VIN is connected by R1 to the V-Sense input of the ASIC, which is an input to an
internal ADC and pulse counting and timing circuits. In analog voltage input mode, resistor R1 is
internally connected to external capacitor C1 on the C-Alias pin of the ASIC. This forms an anti-alias RC
low-pass filter for the ADC.
4-4
Figure 4–2 Typical EAM Channel
SD39EAM-1r4
September 2005