8: Why Do I Get All Zeros When I Read An Analog Value; What Is The "Analog Value Polling Time Out; Conversion To Modbus Rtu; 1: Hardware Configuration - Honeywell HON-CGW-MBB Installation And User Manual

What is the "Analog Value Polling Time Out"?

• The point from which an analog value is being requested is not a 4–20 mA analog
input module.
• At least one of the points in the group of points from which an analog value is being
requested is not a 4–20 mA analog input module.
• More than 10 analog values have been requested in a single request.
7.25.8 Why do I get all zeros when I read an analog value?
There are several reasons a zero reading from an FMM-4-20 Analog Input Module is
received:
• The first read for an analog value from the gateway initializes the polling routine in the
gateway to retrieve analog values from the NFN network. The first response will usually
be all zeros. This is normal. The subsequent polls of an analog value for the same point
or group of points will return actual values. As long as the same points continue to be
polled at a rate faster than the Analog Poll Time Out, then the gateway will continue to
poll the same points.
• The gateway does not actually take an analog value reading unless the module has
reached the first threshold and therefore it will return a zero reading.
• If the client polls the gateway too quickly after the initialization poll then the gateway
may still return zeros.
• If the client polls the analog values slower than the Analog Poll Time Out, then the
gateway may return all zeros.
7.26 What is the "Analog Value Polling Time Out"?
This is how long a gateway will continue to poll analog points after the last client read
request of the points. As long as the client makes analog reads of the same points faster
than the Analog Value Polling Time then the gateway will continue to poll these points. If
the client polls slower than the Analog Value Polling Time then the gateway may return
readings of zero because this will be considered an initialization read.

7.27 Conversion to Modbus RTU

CLSS Gateway (acting as a Modbus slave) interfaces with a Modbus master through
Modbus TCP protocol. For a Modbus RTU master to interface with the CLSS Gateway, use
Moxa MGate MB3180 and convert the Modbus TCP protocol to the Modbus RTU (Serial)
protocol.
7.27.1 Hardware Configuration
Refer to the Moxa MGate MB3180 Quick Installation Guide for hardware configuration of
the MB3180.
CLSS Gateway - Installation and Users' Manual | P/N:LS10248-000HW-E | REV. F | FEB/11/2022
Modbus Communications
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