2-20 Analog Inputs
Example 2:
Consider the following setup:
• [Anlg In Config], bit 0 = “0” (voltage)
• [Speed Ref A Sel] = “Analog In 1”
• [Analog In1 Hi] = 10V
• [Analog In1 Lo] = 0V
• [Speed Ref A Hi] = 50hz
• [Speed Ref A Lo] = 0hz
• [Maximum Speed] = 45hz
• [Minimum Speed] = 15hz
The only change from Example 1 is the [Speed Ref A Hi] is changed to 50
Hz.
The deadband, as it relates to the analog input, can be calculated as follows:
1. The ratio of analog input volts to frequency (Volts/Hertz) needs to be
calculated. The voltage span on the analog input is 10 volts. The
frequency span is 60 Hz.
2. Determine the frequency span between the minimum and maximum
speed limits and the Speed Ref A Hi and Lo.
3. Multiply by the volts/hertz ratio
Here, the deadband is “shifted” due to the 50 Hz limitation. The command
frequency from 0 to 3 volts on the analog input will be 15 Hz. After 3 volts,
the frequency will increase at a rate of 0.2 volts per hertz up to 9 volts. After
9 volts on the analog input the frequency command will remain at 45 Hz.
Motor Operating Range
[Maximum Speed][Minimum Speed]
Command Frequency
Slope defined by (Analog Volts)/(Command Frequency)
Frequency Deadband
Frequency Deadband
15 Hz 45 Hz 50 Hz0 Hz
[Speed Ref A Lo] [Speed Ref A Hi]
10V
0V
[Analog In1 Hi]
[Analog In1 Lo]
0-3 Volts 9-10 Volts
10 Volts/50 Hz = 0.2 Volts/Hz
[Speed Ref A Hi] – [Maximum Speed] = 50 – 45 = 5 Hz and . . .
[Minimum Speed] – [Speed Ref A Lo] = 15 – 0 = 15 Hz
5 Hz x 0.2 Volts/Hz = 1 Volt
15 Hz x 0.2 Volts/Hz = 3 Volts
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