DTL-DB10-6 View Datasheet(PDF) - Murata Manufacturing
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DTL-DB10-6 Datasheet PDF : 14 Pages
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DTL-IFB-485
Interface Board for Serial-Input Electronic Loads
USING THE DTL-IFB-485 SERIAL ADAPTER
WITH DTL2A FAMTILY 100W SERIAL ELECTRONIC LOADS
Overview
The DTL-IFB-RS485 allows up to 256 DTL2A series of serial
100W loads to be operated on a single RS-485 half duplex
cable at distances up to 5,000 feet from the controlling
computer. The DTL-IFB-485 uses serial communication and
can be connected to a standard PC RS232 COM port with an
appropriate RS232/RS485 adapter. Alternatively a plug-in
RS485 board (PCI/ISA) can be inserted in the control
computer. Control of the DTL2A Series load is via ASCII string
commands with ASCII responses. The DTL-IFB-485 includes
a small microcontroller that makes the protocol conversions
between the ASCII commands and the DTL2A2 Series load.
Commands and responses are detailed in Command Syntax
section herein.
The DTL-IFB-485 also includes an uncommitted and optically
isolated 12 bit analog input channel. Dip-switches on the
board allow selection of unipolar ranges of 4.096V (resolution
1mV), 8.192V (resolution 2mV) and 40.96V (resolution 10mV).
The analog input channel might typically be used for
measuring the voltage across the DTL2A load from the U.U.T.
or the current drawn using a shunt, but since it is a free
isolated 2 terminal input, it can also be used for any other
purpose.
Six of the 10 lines are used for power distribution, and the
remaining 4 are used as two pairs for the transmit and
receive RS-485 differential signals. The use of standard flat
10 way I.D.C. cable allows socket connectors to be easily
pressed on the cable at appropriate positions for the loads.
Although 6 conductors are dedicated for power distribution,
standard 28AWG cable has a resistance of 55 ohms/1,000
feet so the voltage drops incurred sending 5V power over a
few tens of feet will be prohibitive. For longer distances, 5V
power should be provided locally at each DTL-IFB-485 and
connected via the screw connector.
Standard RS-485 provides for a fan out of 32 units
on a bus. The DTL-IFB-485 uses special low power driver/
receivers which only present a 1/8 unit load. Consequently up
to 255 devices can be connected to a bus.
The data transmission rate is set on the DTL-IFB-
485 using a 2 position dip switch. Baud rates of 9,600, 2,400,
1,200 and 300 can be selected as shown:
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The DTL-IFB-485 requires +5V power at 100mA. Each
interface board includes screw connections for the 5V power
and the common signal cable can also distribute power to
multiple units.
RS-485 Communication
RS-485 is a similar serial communication standard to the more
common RS-232 found on all personal computers (COM1 &
COM2 ports). The primary difference is that RS-232 uses
single ended transmit and receive data lines with a ±5V to
±15V signal level and as a result, is limited to about 25 feet
transmission distance, whereas RS-485 uses balanced
differential transmit and receive lines with differential
thresholds of +/-200mV and up to +12V and -7V of common
mode voltage. Because of the differential configuration, RS-
485 is much less susceptible to noise than RS-232 and is
specified to operate up to 5,000 feet away from the controller.
True RS-485 is a full duplex system that transmits and
receives on a common 2 wire pair with a ground wire (3 lines).
The DTL-IFB-485 uses a variant of this that has separate
transmit and receive pairs (often referred to as RS-422) plus
ground and power distribution wires. To facilitate connecting
multiple DTL-IFB-485 units and loads to one controller, a 10
way, 0.050" flat cable, is used to interconnect units and the
controller:
Figure 2. Data Transmission Speed Set by Dip-Switches
Generally using 9,600 baud will give the fastest
response and will be the best choice. The data format should
be 8 data bits, 1 stop bit and no parity.
For long distance transmission, over 100 feet,
terminator resistors will improve the performance of the RS-
485 bus. There are several ways of providing termination
matching, but a common method is to place a 120 ohm
resistor across the differential transmit and receive lines at
the far end of the bus. The same configuration can be added
to the transmitting end, but no more than 2 sets of 120 ohm
resistors should be added to a single line.
The schematic of a simple RS-232 to RS-485 converter is
shown in Figure 5, commercial equivalents can be purchased
from many sources.
Figure 1. RS-485 Signal Lines
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