LDM-1000
LVDT/RVDT Signal Conditioning Module
TE CONNECTIVITY SENSORS
/// LDM-1000 OPERATION MANUAL
P/N 09290100-000 REV. C
05/2016
Page 7
4. 4.
Oscillator ‘Sync’ Mode
The Oscillator ‘Sync’ mode setting will depend on the number of LDM
-
1000’s and transducers in
your system, and their physical
locations. For a single LVDT or RVDT system you will be running the LDM-1000 in the Master (INT) mode. For systems with
multiple LDM-
1000’s, especially when they are co
-located, and/or the interconnect cables between the LDM-
1000’s and the
transducers run identical paths, it is recommended to Master and Slave the LDM-1000 oscillators to prevent beat frequencies
and crosstalk between amplifiers and transducers. You will be selecting one LDM-1000 to serve as the Master oscillator (INT),
and the balance will be set-up in the Slave mode (EXT).
CAUTION: Attempting to synchronize two LDM-1000 set as masters (factory default setting) may damage one or both
units. Only one unit can be set to Master mode (INT, SW2 Switch 3 ON), otherwise damage to the electronics may result
(See connection diagrams). All other units must be in the Slave mode (EXT, SW2 Switch 3 OFF).
Connecting Pins 11 (Sync OUT) and 12 (Sync COM) of the barrier strip, from unit to unit, will complete the sync bus circuit (See
connection diagrams). The power common serves as the return line. Use the table below to configure your oscillator mode:
SW2-3
Mode
OFF
SLAVE
ON
MASTER
4. 5. Oscillator Drive Capability
To ensure LVDT/RVDT compatibility with the LDM-1000 you must know the transducer current draw. The LDM-1000 is designed
with a robust sine wave oscillator; it is rated for a maximum drive current of 25mA RMS with a voltage amplitude of 1 or 3 VRMS.
Therefore, you will need to know the LVDT/RVDT transducer input impedance for the frequency at which you intend to operate
it. With the (factory default) 3 VRMS oscillator voltage, the transducer input impedance must be equal to or greater than 120
Ohms, which will result in current draw of 25mA or less. If the impedance of the transducer is lower, the 1 VRMS setting must
be selected; with this setting, the LDM-1000 will be able to operate with impedances as low as 40 Ohms. The input impedance
information is available on the datasheets for all MEAS LVDTs and RVDTs.
4. 6. Setting the Amplifier Gain
You will need to calculate the LVDT or RVDT full scale output, using the simple formula below:
LVDT/RVDT sensitivity (in V/V/inch or V/V/degree), at the selected frequency, multiplied with
the excitation voltage, (1 or 3 VRMS for the LDM-1000), multiplied with
the full scale of the LVDT in inches (or RVDT in degrees).
As an example, the calculation for a MEAS HR1000 LVDT (±1 inch range; 1 inch full scale), with a sensitivity of 0.39V/V/inch at
2.5KHZ, with 3 VRMS excitation would be done as follows:
0.39 x 3 x 1 = 1.17 VRMS full scale output or 1.17 VRMS at ± 1 inch
Using the table below, select the gain settings (switch numbers 6, 7 and 8 of SW1) for the range your full scale output falls into.
In our example, you would use x0.4 HIGH.
Gain 1
Gain 2
LVDT Full Scale
Output, VRMS
Gain
SW1-7
SW1-8
Gain Lo/Hi
SW1-6
x0.4
OFF
OFF
LOW
ON
1.20 to 2.50
x0.4
OFF
OFF
HIGH
OFF
0.78 to 1.20
x1.2
OFF
ON
LOW
ON
0.40 to 0.78
x1.2
OFF
ON
HIGH
OFF
0.26 to 0.40
x3.63
ON
OFF
LOW
ON
0.13 to 0.26
x3.63
ON
OFF
HIGH
OFF
0.10 to 0.13
x4.43
ON
ON
HIGH
OFF
0.05 to 0.10
