Sel SEL-421 - SEL-2600 A RTD Module Operation; Operational Overview; SEL-2600 A RTD Module and the SEL-421; RTD Status Bits

R.5.23
Date Code 20111215 Reference Manual SEL-421 Relay
SEL Communications Protocols
SEL-2600A RTD Module Operation
SEL-2600A RTD Module Operation
The SEL-2600A RTD Module Protocol (RTD) enables communication with
an SEL-2600A via an SEL-2800 (EIA-232 to Fiber-Optic) Transceiver.
Figure 5.1 SEL-2600A RTD Module and the SEL-421
This protocol supports data acquisition of up to 12 temperature channels and
places the results directly into predefined analog quantities (RTD01–RTD12)
inside the relay for use in free-form SEL
OGIC applications. For more
information on the SEL-2600A or SEL-2800, contact your local technical
service center, the SEL factory, or visit the SEL website (www.selinc.com) for
a copy of the SEL-2600A and SEL-2800 product flyers.
Initialization
Perform the following steps to prepare the SEL-421 for communicating with
an SEL-2600A RTD module:
Step 1. Set the desired port to RTD protocol.
Step 2. Set the port setting RTDNUM to the number of RTDs attached
to the SEL-2600A.
Step 3. Set the RTD type settings (RTDnnTY) to the appropriate RTD
type.
Step 4. Connect the SEL-2600A RTD Module to the port via the
SEL-2800 (EIA-232 to Fiber-Optic) Transceiver.
Operational Overview
The SEL-2600A RTD module sends all temperature measurements to the
relay every 0.5 seconds. The relay places the received temperature
measurements into analog quantities RTD01 through RTD12 for use in free-
form SEL
OGIC applications. The data range is from –50 to +250 °C.
If the relay stops receiving valid analog quantities from a certain channel, the
temperature stored in the relay freezes at the last received value. Fifteen status
bits help supervise decisions based on temperature measurements. Table 5.20
describes how to interpret the status bits.
To view the temperature measurements received from the SEL-2600A, issue
the MET T command, as depicted in Figure 5.2.
SEL-2800
SEL-421
SEL-2600A
RTD Module
RTD
RTD
Table 5.20 RTD Status Bits
RTD Status Bit Description
RTDFL Asserts if the SEL-2600A experiences an internal problem.
RTDCOMF Asserts if the relay does not receive a valid measurement from
the SEL-2600A for 1.25 seconds.
RTD01ST–RTD12ST Assert when an RTD is attached to a channel and the
SEL-2600A is able to read RTD.
NOTE: When a channel status bit is
not asserted, the data in the
respective analog quantity is the last
valid temperature, not the current
temperature.