Specifications

Multi-Zone Gas Monitors

56 P/N: 3015-5074 Rev 10

the preset multiple register function. If the transaction is successful, the MZ monitor sends the appropriate

MODBUS response. It is the responsibility of the master device, when making modifications, to insure that

all parameters transferred are within the working limits of the MZ.

IMPORTANT: Each time parameters are modified and sent back to the monitor using

function 16 (preset multiple registers), the new values are written to the monitor's non-

volatile FLASH memory. Due to the finite write life of the FLASH memory device (10K-

100K write cycles), modifying and writing variables should be performed on an “as needed”

basis and not periodically. Exceeding the FLASH write life can result in memory

corruption, requiring a CPU board replacement.

B.3.3. MZ Monitor Polling

After the MZ monitors are setup and operating, the master device need only poll each monitor for its status

detected through the status register and more details are required, additional registers can be examined.

Also if current PPM values are required, the PPM register provides access to current PPM values for all

zones. The MZ monitor requires a minimum of 20 seconds to complete a gas concentration measurement

for a single zone. Therefore, it is not necessary to poll the MZ monitor more frequently than once every 15-

20 seconds, as there will not be any new data available/obtained by more frequent polling. In fact,

excessive polling will slow the operation of the MZ. Under no circumstances should the MZ monitor be

continuously polled at rate faster than 500 ms, as this could result in erroneous readings by the MZ monitor.

B.3.4. Network Topologies

MZ monitors may be connected directly to the MODBUS network or they may be connected to the network

through a Remote Display. In either case, each MZ monitor must have a unique node ID. Up to 15 MZ

monitors can be connected directly to the MODBUS network.

If MZ monitors are accessed via an RD connected to a MODBUS network, the RD “BMS enabled”

parameter must be set equal to “1” via the “RDM SETUP” screen on the Remote Display. The same

commands and registers are used to communicate with the MZ directly or through the RD. If the

communications are through the RD, it monitors each MODBUS message to determine if the message is

intended for one of the MZ monitors it is connected to. If it is, the RD passes the message through to the

MZ monitors. If it is not, the message is not passed through. The RD does not make any modifications to

MODBUS messages. It simply passes the query through to the MZ monitor, and passes the response back

to the MODBUS master. In other words, it allows the MZ monitors to be logically connected to the

MODBUS network, when physically they are connected to the local RD network.

IMPORTANT: It is very important to understand that the RD will only pass messages

through to the MZ monitor when the RD is either in the “SYSTEM” screen or the “ZONE

VIEW” screen. If the RD is in any other screen

, it will return a MODBUS “busy” exception

response (exception code 06).

All RD screens, except the SYSTEM and ZONE VIEW screens, have a 10 minute timeout interval. After

this, the screen will return to the SYSTEM or ZONE VIEW screen, depending on which one was last

displayed. The RD may also be password protected so that a password entry is required in order to view

screens other than the SYSTEM or ZONE VIEW screen.

B.3.5. Key Comm Protocol Parameters

Parameter Description

MODBUS Mode RTU only

MZ Baud Rate Default is 19,200. Programmable as defined in system data register.

Parity No Parity