Dynalco SWT-2000 Speed Switch/Speed Transmitter - Manual (Page 12)

Operating Instructions SWT-2000 DYNALCO
8
3. Principle of Operation
3.1 General
The model SWT-2000 is microprocessor controlled and operates in accordance with the period measurement
principle whereby the duration of the input period is measured during the measurement interval. The reciprocal
value based on the average input period corresponds to frequency and hence speed. The relationship
between frequency and speed is determined by the Machine Factor.
The status of System Limits is based on various inputs that can be logically combined AND or OR. System
Limit inputs may be: both speed inputs, a Math function based on the speed inputs and, the 2 binary inputs. A
hysteresis may be set for the speed inputs and Math function individually. The 6 System Limits in each of 4
parameter sets may be individually defined. Parameter sets may be selected via binary inputs. The 4 relays
and 2 open collector outputs may be assigned to any System Limit and will react accordingly. The 2 open
collectors may alternatively be assigned to frequency x1, x2 or x4. Relay and open collector status may be
latched and then reset via binary input.
The system permanently monitors itself. Sensors may in addition be monitored. Sensor error may be used in
the configuration to influence System Limits. System error would influence the relays, open collectors and
Analog outputs and the front panel LED would go out.
Frequency outputs (Open Collector Outputs) are not influenced by the Machine factor but correspond to the
input signal. For frequency X2 or X4 the 2 input signals should ideally be phase shifted by 90 degrees.
Parameter input is via resident PC software and the Ethernet Interface. This may also be used to interrogate
the unit, display measurement and unit status.
The Parameters are safely stored in EEPROM.
3.2 Machine Factor
The machine factor establishes the relationship between sensor frequency (Hz) and corresponding speed
(RPM).
Machine Factor = Frequency
RPM
If the # gear teeth and RPM are known, use the following formula to calculate corresponding frequency:
Signal Frequency (Hz) = (RPM) X (Teeth or Discontinuities)
60
Another way to calculate the machine factor is:
Machine Factor = (Teeth or Discontinuities)
60
Note: The above formulas are based on the gear or target turning at the same speed as the machine being
monitored, ie: no step up or step down gear ratios involved.