VMC 186/40 Motion Hardware Information
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Magnetostrictive Transducer Interrogation Pulse Polarity
(Default positive polarity)
Jumpers P4-P7 are used to select the polarity of the magnetostrictive transducer interrogation pulse. The
motion controller is shipped with all four axes configured for positive interrogation pulses. Transducers can be
ordered with either positive or negative interrogation pulses. Usually, the 1 foot transducers or shorter come
with negative interrogation pulses. We recommend ordering only positive interrogation pulse for system
consistency.
Note: If the VMC 186/40 is connected to a negative interrogation pulse transducer when it is configured for
positive interrogation pulses, current limiting resistors on the VMC 186/40 will burn out. The current limiting
resistors protect the transducer rod and are field replaceable.
Jumpers P4-P7
P4 1-2 axis 1 positive pulse
P6 1-2 axis 3 positive pulse
P4 2-3 axis 1 negative pulse
P6 2-3 axis 3 negative pulse
P5 1-2 axis 2 positive pulse
P7 1-2 axis 4 positive pulse
P5 2-3 axis 2 negative pulse
P7 2-3 axis 4 negative pulse
1
2
3
1
2
3
P4 P5
1
2
3
1
2
3
P6 P7
Number of Recirculations
Recirculation is a term used with magnetostrictive transducers. It indicates how many times the transducer is
interrogated for a single distance measurement. If recirculation is set to one, only one interrogation pulse is
issued. If it is set to four, then four interrogation pulses are issued.
The trade-offs are measurement speed, resolution, and transducer length. The higher the number of
recirculations, the higher the resolution, the slower the speed and the shorter the transducer length. The lower
the number of recirculations, the lower the resolution, the faster the speed, and the longer the transducer rod.
See the following tables.
Transducer Delay per Inch (9.1us typical)
Counts Per Inch =
* Recirculations
18ns per clock (55.5 Mhz clk)
65535
Maximum Linear Transducer Length =
Counts per Inch
Longest Measurement Time = Transducer Length in Inches * Delay * Recirculation
Inch
Maximum Resolution =
Counts per Inch
