Specifications

GENERAL DESCRIPTION & BLOCK DIAGRAM
The DGH D3000/4000 series are complete computer-to-
analog output interfaces. They are designed to be
mounted remotely from a host computer and communi-
cate, in ASCII, with standard RS-232 and RS-485 serial
ports. Simple ASCII commands are used to control a 12-
bit DAC (Digital-to-Analog Converter) which is scaled to
provide commonly used current and voltage ranges. An
8-bit CMOS microprocessor provides an intelligent
interface between the host and the DAC.
The DGH modules are easy to use. You do not need
engineering experience in complicated data acquisition
hardware. This modular approach to data acquisition is
extremely flexible, easy to use and cost effective. The
modules can be mixed and matched to fit the application.
They can be placed remote from the host and from each
other. You can string up to 124 modules on one set of
wires.
Figure 1 shows a functional block diagram of the D3000/
4000. The DAC converts digital data derived from host
commands into the desired analog output. The micropro-
cessor receives commands and data from the host
computer through an RS-232 or RS-485 port. A wide
variety of two-or-three-letter commands from the host
control the DAC, read status information, and configure
the module to fit your requirements. Responses to
commands are produced by the microprocessor and
transmitted back to the host over the serial link.
For example, the module's analog output is controlled by
the Analog Output (AO) command from the host. The
host command/module response sequence looks like
this:
Command: $1AO+00010.00
Response: *
If a 0-20mA output module is used for this example, the
AO command produces a 10mA output. The module
performs the output function and responds with a '*' as an
acknowledgement that the command has been per-
formed.
In response to host commands, the microprocessor
produces the appropriate digital data necessary to control
the DAC. Digital data is transmitted to the DAC through
opto-isolators that provide electrical isolation. The DAC
produces a precise analog current that is directly propor-
tional to the magnitude of the digital data. The DAC
output current is processed and amplified by signal
conditioning circuits to produce the desired output voltage
or current. Output protection circuits protect the module
from potentially damaging output faults.
An EEPROM (Electrically Erasable Programmable Read-
Only Memory) retains important data such as the ad-
dress, baud rate, parity and calibration data even if the
module is powered down.
The D4000 series features an 8-bit ADC (Analog to
Digital Converter) that monitors the output signal. The
ADC input is tied to the analog output and converts the
signal level to digital data. The digital data is optically
isolated and may be read by the microprocessor. The
ADC allows the user to monitor the output signal and
ensure its integrity.
The power supply converts the raw 10 to 30V input power
into regulated voltages used to operate the module. The
power it supplies to the DAC and output circuits is
transformer isolated from the input power and communi-
cations connections. The transformer and opto-isolators
provide an isolation barrier between the output section
and the rest of the circuitry. The isolation barrier is helpful
in breaking ground loops, isolating troublesome common-
mode voltages and protects the host and module in
cases where the output may accidentally contact AC
power lines.
The combination of an accurate high-resolution DAC and
a dedicated microprocessor produces a very powerful
system for generating process control signals. The
microprocessor provides software addressing for mul-
tidrop capability, data formatting in engineering units, limit
checking, digital calibration and many other features not
possible with unintelligent analog output systems.
The D3000/4000 are compatible with the DGH D1000
and D2000 series and may be mixed in any order.
All modules are supplied with screw terminal plug con-
nectors and captive mounting hardware. The connectors
allow system expansion, reconfiguration or repair without
disturbing field wiring.
UTILITY SOFTWARE
Complimentary Utility Software is included with each
purchase order. The software is compatible with Windows
95, 98, NT 4.0+, 2000 operating systems and distributed
on CD-ROM. The Utility Software simplifies configuration
of all user-selectable options such as device address,
baud rate and filtering constants. The latest version of our
software is always downloadable from our web site at
www.dghcorp.com.
Figure 1. D3000/4000 Block Diagram.