Ectron 451, Instruction Manual

Page: 39 / 74

Similarly, when at the EXAMPL MODE SETUP screen, pressing the screen will display
EXAMPL POINT1 VOLTS
if the Example mode is active or it will display
EXAMPL
ACTIVE ? NO
if it is not active.
To determine if the scale mode is active, go to the
SCALE MODE SETUP
screen. Pushing
this display will show the screen
SCALE POINT1 VOLTS
if scale mode is active. If it is
not active, SCALE ACTIVE ? NO will be shown.
CROSSTALK
Crosstalk between LVDT/RVDT transducers occurs when the excitation from one sensor
mixes with the data signal from another. The result is that the output dc signal is modulated,
usually by the difference frequency of the two excitation supplies. Depending on the difference
frequency, the modulation can be a very low frequency. For unshielded sensors, when crosstalk
occurs, the output signal will vary by this difference frequency.
Since the excitation supply of the Model 451 can provide 30 mA of current, generally two
or three LVDT or RVDT transducers can be connected in parallel and excited by one Model
451. This would eliminate the cross talk problem. Check primary impedance to determine
how many loads can be supported by a single excitation supply. A higher excitation frequency
or a lower voltage would increase the impedance thereby reducing the current required by
each transducer.
If it is necessary to operate the sensors in close proximity to different excitation supplies,
shielding can be added to the transducers to minimize the crosstalk effect. A single wrap
of a good shielding material will usually reduce the crosstalk to an acceptable level. For
additional help, consult factory.
OUTPUT NOISE
The filter settings of WB (wideband), 100 Hz, 10 Hz, and 1 Hz can be used to reduce input
signal noise but will not help reduce output noise. If speed of response is not required,
output noise can be reduced by adding an output filter following the Model 451. An rc filter
consisting of a 10 k
Ω
series resistor and a 1
µ
F shunt capacitor to common will reduce any
noise considerably. See Figure 4-1.
PHASE CONTROL
One of the design features of the Model 451 is that it does not require a phase control. The
phase of the incoming signal is derived from the signal applied to the differential amplifier.
Thus, this conditioner is not susceptible to phase changes of the cabling or the phase non-
linearity of the transducer.
GROUND CONNECTIONS
Case ground (Pin 13) should be connected to the common of the input power (Pin 15) and,
if possible, to earth ground. (This is automatically taken care of in Ectron enclosures.) This
connection will allow the emi (rfi) filters of the Model 451 to maximize the rejection of
high-frequency noise signals. It is further recommended that excitation low (Pin 14) and
output common (Pin 11) be connected to this point. However, output common can be floated;
so if the load has a different grounding point, Pin 11 should be connected to load common.
Whether this common point should then be connected to earth or power ground depends
on where output noise is minimized.
Model 451 Applications
4-5