Precision Digital PD8-765 - Manual (Page 26)

PD8 Series Explosion-Proof Instrument Supplemental Manual
26
Digital I/O
Digital inputs and outputs are only present on ProtEX-MAX models with integrated
P
RO V U functionality. See Model Number Descriptions on page 4 for details on which
instruments qualify.
The ProtEX-MAX has four digital inputs and four digital outputs. External digital
inputs can function similarly to the front panel function keys.
!
NOTICE
The digital inputs are configured at the factory to function identi-
cally to the front panel pushbuttons in order to work with the
SafeTouch buttons. Changing the programming of the digital in-
puts will affect the function of the SafeTouch buttons.
They can be configured to trigger certain events (i.e. acknowledge/reset alarms, reset
max and/or min values, disable/enable all output relays, and hold current relay
states), provide direct menu access point, or mimic front panel keys.
Digital outputs can be used to remotely monitor alarm relay output states, or the
states of a variety of actions and functions executed by the meter.
See the P RO V U Instruction Manual included with this instrument for details on
programming the Digital I/O.
Serial Communications Overview
RS-232 and RS-485 are standard interfaces approved by the Electronic Industries
Alliance (EIA) for connecting serial devices. In EIA terms, the device (e.g. meter) that
connects to the interface is called a Data Communications Equipment (DCE) and the
device to which it connects (e.g. the computer) is called a Data Terminal Equipment
(DTE).
RS-485 can support multi-point connections per line because it uses lower-
impedance drivers and receivers.
Line drivers and receivers are used to exchange data between two or more points
(nodes) on a serial communications network. Reliable data communications can be
difficult in the presence of induced noise, ground level differences, and other hazards
associated with installation of a network. When communicating at high data rates, or
over long distances in real world environments, RS-232 is often inadequate. The
differential data transmission of RS-485 offers superior performance in most
applications. Differential signals can help nullify the effects of ground shifts and
induced noise signals that can appear as common mode voltages on a network.
A multi-point network consists of multiple drivers and receivers connected on a single
bus, where any point (node) can transmit and/or receive data. RS-485 allows multiple
drivers and receivers on the same two-wire or four-wire system. The RS-485
standard specifies up to 32 drivers and 32 receivers on a single bus, but with the