User's Manual

V740 RFID READER/WRITER, ANTENNA 2005-07, REV.01
OPERATION MANUAL
27 of 45 ©OMRON CORPORATION 2005
(See 3.2 Communications Time)
The constraints on the scheduler in the reader for the
time_out are shown below. Time is equally divided
among the specified protocols. The reader searches
sequentially for each antenna in the time provided for
the protocol. When the last antenna completes
searching, the reader returns to the first antenna
again. Following chart shows an example of time
schedule given by the model command as below.
SELECT id FROM tag_id WHERE
(protocol_id='protocol1' or
protocol_id='protocol2') and
(antenna_id=ant1 or antenna_id=ant2);
The antenna arbitration algorithm is optimized to
maximize the read rate of all the tags in the field. For
EPC0, each antenna will be given 150ms of search
time. The time division for each antenna within a
protocol is determined automatically by the reader and
cannot be specified by the user.
It is important to specify the protocols in the RQL
commands, if no protocol is specified, the reader
searches for tags using all possible protocols,
resulting the slower read rates. When specifying
multiple protocols, calculate the minimum time_out
value using the following calculation.
minimum time_out = max{# of protocol 1 tags x
read time of (1) tag), (# of protocol 2 tags x read
time of (1) tag),..} x ( # of protocols) x (# of
antennas) (ms)
e.g. if 40 EPC0 tags takes 450 ms (cf. 3.2
Communications Time) and 10 EPC1 tags takes
20 ms per tag on average. With two antennas:
minimum time_out =
max{450, 10 x 20} x 2 x 2 = 1800 ms.
As another example, if the goal is to search for EPC1
and EPC0 tags on antennas 1, 2 for 20 strong tags on
each protocol. The query specified is;
SELECT read_count, protocol_id,
antenna_id, id FROM tag_id WHERE
(antenna_id = 1 OR antenna_id = 2)
AND (protocol_id='EPC1' OR
protocol_id='EPC0') SET
time_out=700;
EPC0 and EPC1 will each get a 350 ms slot. This will
allow all 20 EPC0 tags to be read, but not all EPC1
tags.
If the EPC0 tags are present only on the 2nd antenna,
the reader will never arbitrate time to this antenna. A
better query would be:
SELECT read_count, protocol_id,
antenna_id, id FROM tag_id WHERE
(antenna_id = 1 OR antenna_id = 2) AND
(protocol_id='EPC1' OR
protocol_id='EPC0') SET time_out=1600;
EPC1 EPC0
350 ms 450 ms
ant1 ant2 ant1 ... ant1 ant2 ant1
EPC1 EPC0
800 ms 900 ms
ant1 ant2 ant1 ... ant1 ant2 ant1 ...
time_out
1600 ms
time_out
700 ms
ant1 ant2 ant1 ... ant1 ant2 ant1 ...
protocol 1 protocol 2
time_out
Both EPC0 and EPC1 will get 800 ms:
each antenna for EPC0 will get 400 ms (above
150ms) should read all 20 EPC0 and 20 EPC1.
Note: It is caused by following reasons that difference
between the time_out value actual time required for
reading.
1. It spends 20 ms to switch protocols.
2. It is fixed on 150 ms to read EPC0 tag.
The max of the difference can be calculated by
summing up the time caused by the reasons. You
need consider time lag to avoid mutual interface due
to time sharing.