Magnetrol Jupiter JM4, Operating Manual

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41-621.1 HART ® to Modbus ® Adaptor Operating Manual
8.
Modbus RTU Communication in HMA Mode
8.1.
Purpose
This procedure instructs how to configure the HART to Modbus Adaptor (HMA), when in the HMA
mode, to support the various registers defined for one or multiple devices attached to a single HMA.
In the HMA mode (register 3007 set to 0), the HMA will be the only device directly visible to the
Modbus RTU/master. This mode can be useful when more devices are attached to the same RS-485
line then there are available Modbus addresses. With each HMA supporting up to 5 HART devices, far
fewer Modbus addresses are required for a given number of HART devices. All commands to read or
write to a device are accomplished by using only HMA registers. In effect, the HART devices will
invisible to the Modbus master, and the HMAs will appear to be able to provide multiple level readings.
For the attached devices, the HMA register number to access various parameters in the attached HART
devices will be different from HART device to HART device and will depend on the slave number of the
device on the HMA.
The following procedure is an example of connecting two HART devices to a single HMA.
8.2.
Equipment
Item Manufacturer Model
HART to Modbus Adaptor MII 031-2859-001
RS485 Communications cable FDTIchip USB-RS485-WE
Termination resistor - 120

Modbus host application www.modbustools.com Modbus Poll
Power Supply - 20-24V, 0.5A
Level transmitter MII Model 706
Probe MII Model 706 compatible
Level transmitter MII Model 705 3x
Probe MII Model 705 3x compatible
Level transmitter MII Model 355
Level transmitter MII Model R82 R2
Level transmitter MII Model RX5
Level transmitter MII Enhanced Jupiter
Level transmitter MII E3 Modulevel
8.3.
Setup
8.3.1
Single HMA
Connect an HMAs to a power supply via the power terminal block. Connect an RS-485
communications cable to a PC which has a Modbus host application. Connect the other end
of the cable to the RS-485 terminal block of the HMA1. Connect a 120

resistor between
the two RS-485 terminal block positions. Connect additional supported Magnetrol HART
devices to the HART loop terminal block of the HMA. There can be any combination of
devices including the Model 706, Model 705 3x, Model 355, Model R82 R2, Model RX5,
Enhanced Jupiter and E3 Modulevel. Note that
each device’s Poll Address can be set to any
value between 1 and 62 as long as it has a unique address from others connected to the
same HMA, and there can be a maximum of 5 devices connected to an HMA including the
device in the housing containing the HMA.
It is suggested that the devices’ poll addresses