Baldor BC141 Installation & Operating Manual page 14

Seven (7) Volt per 1000 RPM Tachometer
Connect the tachometer positive lead (+) to Terminal T and the negative lead (-) to Terminal I2.
Figure 2-8 DC Tachometer Connection (7 Volts Per 1000 RPM)
Fifty (50) Volt per 1000 RPM Tachometer
Connect the tachometer positive lead (+) to Terminal B and the negative lead (-) to Terminal I2.
Figure 2-9 DC Tachometer Connection (50 Volts Per 1000 RPM)
Other Tachometer Voltages
The tachometer input circuit is designed for a 7 Volt or 50 Volt per 1000 RPM DC tachometer used
with an 1800 RPM motor. For a tachometer other than 7 Volts or 50 Volts per 1000 RPM, or for a motor
other than 1800 RPM, an external 1/2 Watt resistor (RT) must be installed. Install RT in series with the
tachometer.
Connect one end of RT to Terminal T, connect the other end of RT to the tachometer positive lead (+),
and connect the negative lead (-) of the tachometer to Terminal I2.
The value of RT Ω can be calculated using the following formula: RT = (1.3 X VT X S) - 16000 Ω
VT is the tachometer voltage (in Volts per 1000 RPM) and S is the base speed of the motor (in RPM).
Example: If a 20 Volt per 1000 RPM tachometer is to be used with a 3600 RPM motor:
RT = (1.3 X 20 X 3600) - 16000 = 77600 Ω
Choose the closest 1/2 Watt resistor value, which is 75000 Ω (75 kΩ).
MN704
Terminal "T"
B
T
Terminal "I2"
Terminal "B "
B
T
I2
Figure 2-10 Other DC Tachometer Connection
B
T
+
7V
G
1000
-
I2
DC Tachometer
+
50V
G
1000
-
DC Tachometer
RT
+
G
-
I2
DC Tachometer
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