Engine Overspeed: Calibration DYNALCO SW-50 Speed Switch

Dynalco SW-50 (Two-Setpoint)

Figure 1.1 - Dynalco SW50-1

→Input Signal = Two input frequency ranges 0-5000 Hz (std. 0-10000 Hz).
→Input Power = 8-32 Vdc (Operates with 12 or 24 Vdc systems).
→Relays = SPDT for Overspeed Relay, SPST N.O. contacts for Auxiliary Relay. Setpoint adjustment range for both relays: 3–100% of full-scale frequency range. Integral 25-turn trim potentiometer for each relay setpoint. 

At stand-still (zero speed), and power ON, the standard relay configuration is:
1). Overspeed Relay: SPDT, normally energized. Relay de-energizes and latches on overspeed. Latching may be inhibited by jumpering Terminal 4 to Terminal 2 (re-setting is then automatic).
2). Auxiliary Relay: Normally de-energized. Relay energizes above the setpoint, non-latching (automatic reset).

→Resetting relays:
a). The latched Overspeed Relay is reset (after speed is reduced by at least 2% below setpoint value) by momentarily jumpering Terminal 4 (Overspeed Reset/ Latch Inhibit) to Terminal 2 or by momentarily removing power.
b). The Auxiliary Relay will automatically reset when speed is reduced by at least 2% below setpoint value.

Jumpering Terminal 5 (Test) to Terminal 2 lowers the setpoints to 90% ±2% of the actual value to permit verifying the alarm setpoints without overspeeding the Engine.
Figure 1.2 - Engine Overspeed Test

#Verify Current Calibration:
1). Connect a signal generator to the SW-50 magnetic pickup input (Signal Input).
2). Set the signal generator to a low frequency. Slowly increase the frequency. Using an ohmmeter across each relay contact, in turn, determine the frequency at which the relays change state (Note: Overspeed Relay will latch if terminal 4 is not grounded).
Figure 1.3 - Verify Overspeed (Test)

#Change the Setpoints:
1). Remove the screws in the access holes for the relay adjustment trim pots.
2). Set the signal generator to the frequency at which the relay should change state.
3). Using a small/ flat screwdriver, adjust the trim pot for the appropriate relay until the relay changes state.
Figure 1.4 - Adjust the trim pot
4). Decrease the frequency, and then slowly increase it to verify that the relay trips at the appropriate point.

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