CGW-MB Installation and Users’ Manual | P/N:LS10248-000HW-E | REV.G | JUL/31/2022
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What is the “Analog Value Polling Time Out”?
Modbus Communications
7.24.6 How many analog values can I read at a time?
Ten analog values can be read at one time. An initialization read must be performed.
7.24.7 Why do I get an exception code when trying to read an analog value?
There are several reasons why an exception code is received when requesting an analog
value:
•
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.
7.24.8 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 CLSS Gateway mainboard initializes the
polling routine in the CLSS Gateway mainboard 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 CLSS Gateway mainboard will continue to poll the
same points.
•
The CLSS Gateway mainboard 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 CLSS Gateway mainboard too quickly after the initialization poll
then the CLSS Gateway mainboard may still return zeros.
•
If the client polls the analog values slower than the Analog Poll Time Out, then the
CLSS Gateway mainboard may return all zeros.
7.25 What is the “Analog Value Polling Time Out”?
This is how long a CLSS Gateway mainboard 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 CLSS Gateway
mainboard will continue to poll these points. If the client polls slower than the Analog
Value Polling Time then the CLSS Gateway mainboard may return readings of zero
because this will be considered an initialization read.
7.26 Conversion to Modbus RTU
CGW-MB (acting as a Modbus slave) interfaces with a Modbus master through Modbus
TCP protocol. For a Modbus RTU master to interface with the CGW-MB, use Moxa MGate
MB3180 and convert the Modbus TCP protocol to the Modbus RTU (Serial) protocol.
7.26.1 Hardware Configuration
Refer to the
Moxa MGate MB3180 Quick Installation Guide
for hardware configuration of
the MB3180.