Date Code 20010518 “Job Done” Examples - (Example 8) 4-61
SEL-2020 Instruction Manual
EXAMPLE 8: GETTING DATA FROM A NON-SEL IED
Example 8 demonstrates the SEL-2020’s ability to communicate with non-SEL IEDs using the
nearly universal EIA-232 communications interface. The EIA-232 interface is a standard with
specified electrical signal parameters that ensures compatibility between two devices. For
devices that use this standard, you must know how to make the proper electrical connection
between the two devices to permit communication. Additionally, each of these devices must
recognize the “language” that the other “speaks;” therefore, you need the “dictionary,” or
command set, that defines each language.
In this example, the SEL-2020 communicates with a DGH 1000 RTD Interface Module. This
example assumes that you have connected the DGH 1000 to Port 12 on the SEL-2020, as shown
in Figure 4.11, using the proper cable, and that you know the communication parameters (baud
rate, data bits, parity, stop bits, and flow control) required by the DGH 1000. The example also
assumes that you have the command set, or “dictionary” of terms, for each device. In this case
you know that when you send the message string “$1RD” to the DGH 1000, the device returns
the temperature as an ASCII floating-point number.
SEL-251
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SEL-251
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SEL-251
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Optional
Modem
Port 8
Port 7Port 6Port 5Port 4Port 3Port 2Port 1
SEL-2020
Port 2R
Telephone
Line
DWG: 2020_16.vsd
Local
Terminal
Port F
Cable
C234A
DGH
1000
Port 12
Port 2R Port 2R
Port 2R Port 2R Port 2R
Figure 4.11: Non-SEL IED Attached to Port 12
IDENTIFYING THE PROBLEM
Your objective in this example is to use the SEL-2020 to retrieve temperature data from a remote
thermal device (RTD) interface module called the DGH 1000. The DGH 1000 is connected to
the SEL-2020’s Port 12 and you want to collect these data every 30 seconds.
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