Other signal modules
7.4 Position decoder module SM 338; POS-INPUT; (6ES7338-4BC01-0AB0)
S7-300 Automation System Module data
Manual, 08/2006, A5E00105505-04
7-9
Wiring rules
Important rules to observe wiring the module:
● Ground of the encoder supply is connected to CPU ground potential. Thus, establish a
low impedance connection between pin 2 of SM 338 (M) and CPU ground.
● Always use shielded twisted-pair cable to wire encoder signals (pins 3 to 14.) Connect
both ends of the shielding. Use the shield connection element to terminate the shielding
on SM 338 (order number 6ES7390-5AA00-0AA0.)
● Connect an external power supply if the maximum output current (900 mA) of the
encoder supply is exceeded.
Technical data of SM 338; POS-INPUT
Technical data
Dimensions and weight
Dimensions W x H x D (mm) 40 x 125 x 120
Weight approx. 235 g
Voltages, currents, electrical potentials
Rated load voltage L+
• Range
• Reverse polarity protection
24 VDC
20,4 ... 28.8 V
No
Electrical isolation no, only to shield
Permissible potential difference
• between the input (M terminal) and CPU grounding
busbar
1 VDC
Encoder supply
• Output voltage
• Output current
L+ -0.8 V
max. 900 mA, short circuit-proof
Current consumption
• from the backplane bus
• from load voltage L+ (no load)
max. 160 mA
max. 10 mA
Power loss of the module typ. 3 W
Encoder inputs POS-INPUT 0 to 2
Position detection absolute
Difference signals for SSI data and SSI clock to RS422 standard
Data transfer rate and cable (twisted-pair and shielded)
length of absolute value encoders
• 125 kHz max. 320 m
• 250 kHz max. 160 m
• 500 kHz max. 60 m
• 1 MHz max. 20 m
SSI frame transfer rate
• 125 kHz
• 250 kHz
• 500 kHz
• 1 MHz
13 bits 21 bits 25 bits
112 µs 176 µs 208 µs
56 µs 88 µs 104 µs
28 µs 44 µs 52 µs
14 µs 22 µs 26 µs
Monoflop time
2
16 µs, 32 µs, 48 µs, 64 µs
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