New
functional safety incremental encoders from Pepperl+Fuchs use a sine/cosine
output interface to measure speed, rather than traditional square waves, to
create a decentralized safety solution for use with safety speed monitoring
PLCs and relays.
The
RVS58S
encoder is the first and only ISO13849 certified SinCos encoder
specifically designed for use in safety aligned systems up to SIL3 (IEC 61508,
IEC62061), performance level "e" (IEC 13849). The encoders are also suitable as
a motor feedback system for safe drives in accordance with IEC 61800-5-2. Functional
safety requirements like Safe Limited Speed (SLS), Safe Torque Off (STO), Safe
Operating Stop (SOS), Safe Stop (SS1, SS2), Safe Direction (SDI) and further
safety functionality can be realized without redundant sensors.
Because
the SinCos interface is compatible with existing safety PLC products, safety
controllers that implement cable break detection technology and verification
checks on the input signals can achieve the highest degree of safety. The
rotary encoders also provide internal self diagnostic features to verify the
calculated output, along with additional temperature and voltage checking safe
diagnostic features.
According
to David Rubinski, a product manager for Pepperl+Fuchs, sinusoidal feedback
provides continuous wave forms and the technology offers a mechanism to detect
wire breaks, a key issue and limitation with incremental encoders.
"When
an encoder is functioning correctly and there is no wire break, the safety
device connected to the encoder can look at the sine-cosine waves and calculate
whether or not the signal is genuine, uninterrupted and reliable," says
Rubinski. "Since sine squared plus cosine squared equals one, the connected
device can calculate whether or not the signal is functionally safe."
Since
the connected system is a safe device which can calculate and verify that the
two signals are proper, if there is anything wrong with the signal, the
controller can determine that condition and take appropriate action. The big
problem with using standard incremental encoders is that there are no check
mechanisms because at zero speed the square wave signal could be either high or
low. But with a SinCos encoder, the outputs can still be verified to determine
if the signals are proper at zero speed.
The
big benefit for customers is a system that offers cost and time-savings by
allowing for higher machine availability and productivity. The encoders can
also be directly attached to a motor due to temperature resistance up to 115C.
The
RVS58S encoders offer 1024 or 2048 signal periods and are thermally stabilized
for high resolution interpolation. They operate at 5V dc (Β±5 percent) and
deliver a 1 Vpp output signal up to a maximum output frequency of 200 kHz in
operating temperatures ranging from -20 to 80C.
They are rated to handle axial shaft loads of 40N at a maximum of 6,000
RPM or 10N at a maximum of 12,000 RPM. Maximum radial shaft loads are 60N at
6,000 RPM or 20N at 12,000 RPM.
Targeted
applications for this new safe encoder technology include motor and drive speed
monitoring, elevators, theater stage equipment, cranes, storage robots and
printing.
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