MODEL 36, TYPE B & C
SINGLE RANGE TENSIONCELLS
INSTRUCTION MANUAL A-279
2
Copyright 2023 - Revised Comptrol All Rights Reserved
For our discussion here, deflection of the Load Plate
toward the Base Block is defined as the "Compression
Mode", while the opposite is defined as the "Tension Mode".
Tensioncells are designed to operate equally well ineither
mode.
The Base Block contains an integral Mechanical Stop to limit
the amount of deflection in either direction, and a Viscous
Damper to allow control of the Tensioncell response to rapid
changesinapparent tension loads. (SeePage1, Figure 3)
I-C THE ELECTRICAL SYSTEM
The electrical system consists of a Linear
Variable Differential
Transformer
(LVDT) which converts the mechanical deflection
of the Load Plate into a useful electrical output signal. (See
Figure 4) The movable core of the LVDT is mechanically
coupled to the Load Plate by means of the Core Adjust
Assembly.
(See Figure 4.) This adjustment
is factory set and
is
not accessible.
I-D TYPE “K” DC LVDT
As illustrated in Figure 4, a DC LVDT consists of the
following components:
•An oscillator network, which converts the DC
input voltage into a high frequency alternating
current for exciting the Primary Coil (P1).
•A Primary Coil (P1).
•A movable, permeable metallic core.
•Two Secondary Coils (S1and S2).
•A demodulator and summing network to rectify
and integrate the currents from the Secondary
coils.
With Comptrol LVDTs, the input and output circuits are
electrically isolated from each other and from the
mechanical structure of the Tensioncells. Thus, they
may be used in “floating ground”or “ground return”
systems. This eliminates the need for extra circuit
boards which are required for most strain gage loadcells.
Tensioncells are factory adjusted to provide an offset
voltage with no load applied (no deflection). Using an
input of 24 volts DC, the LVDT is set to provide an
output of 3.5 volts into a resistive load of not less than
100,000 ohms. The voltage resulting from the maximum
rated deflection then adds to or subtracts from the 3.5
volt offset. This results in an output voltage of 3.5 to 6.5
volts in the Compression Mode and 3.5 to 0.5 volts in the
Tension Mode. (See Figure 5)
While acceptable performance may be obtained over an
input voltage range of 6.0 to 30.0 volts DC, the output
voltage will vary in direct proportion to the input voltage.
Because of this, the use of a “well regulated” constant
voltage power supply is essential for accurate and
repeatable tension measurement.
In standard applications, where two Tensioncells are
used, the inputs may be connected in parallel allowing
the Tensioncells to be excited from the same power
supply. The LVDT outputs are then summed to obtain a
signal representing the strip tension and tare loads
distributed across the roll
Comptrol Tensioncell Indicators supply 24volt DC and
integrate the output signals in a summing amplifier. This
permits incorporation of additional circuitry for offset and
tare adjustments, as well as adjustments for balance and
gain.
