Solartron Mobrey 7828, Technical Manual

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7828 Density Transmitter Technical Manual Electrical Installation
78285000_AB
3-11
3.4.4 RS485 MULTIDROP
When several devices are connected in parallel on an RS485 network, this is known as
multi-drop. Although it is theoretically possible to have up to 256 devices, in practice this is
limited to around 32 or less, depending largely on the driving power of the Master. Each
device has a unique slave address. For 7828 this address must be individually
programmed, using the ADView software running on a PC, before being connected to the
multi-drop network (see section 4.4.3 for details).
Wiring is quite straightforward: simply connect A terminal to A terminal, B to B. On some
devices, the RS485 signals may be and -. The + signal generally corresponds
to the A signal, and the - signal to B.
3.4.5 TRANSMISSION MODE
The 7828 RS485 interface uses the following parameter settings, which are not
selectable:
Baud rate: 9600
Bits: 8
Parity: None
Stop bits: 2.
3.4.6 ANALOG 4-20MA OUTPUT
The 4-20mA output of the 7828 can be configured to be proportional to a user-defined
range of either density, base or referred density, temperature, or one of the special
functions. Fault conditions within the 7828 are indicated by a 2mA output. If this is
detected, the Modbus link can be used to interrogate the transmitter to establish the likely
cause of the problem.
The 4-20mA output is isolated (floating) from the power supply of the 7828, and can
therefore be connected to any power supply/current measuring device, within the limits
stated in the specification, i.e., 15 to 28V dc at the 4-20mA terminals of the 7828.
A power supply is also required for the 7828 itself, but this can also power the 4-20mA
loop, if appropriate.
Two typical configurations to the analog output are shown below.