MODEL 635
DESCRIPTION
FUNCTION:
The Model 635 Strain Gage amplifier is used to condition strain gage signals and to provide precise, low-
noise excitation voltages to the strain gage(s).
CONSTRUCTION:
The amplifier uses modular construction. Seven modules can be accommodated in a rack adapter,
Encore Model 4007-137. The rack also accommodates a Model 843 power supply module. This module provides
unreg,-24VDC for the amplifier circuitry, plus seven is,-24VDC outputs for the bridge excitation circuits.
FEATURES:
A number of parameters and operating modes are selectable with the front panel controls. Automatic bridge
balance with battery backup is standard. Selectable parameters include cal-select resistors, gain, frequency response,
internal bridge-completion components, and bridge excitation voltage. Selectable modes include AC/DC coupling, internal
DC CAL, external CAL, and ZERO. The ZERO position allows the operator to null the amplifier and to evaluate noise
attributable to the amplifier. An ON/OFF switch for bridge excitation enables the operator to evaluate noise pick-up
attributable to gauge installation (Switch Off) and signal (Switch On).
A mode switch is provided to select the bridge configuration, including 1/4 static, 1/2 static, 1/4 dynamic, and full bridge.
An additional position selects the EMF input mode for operation of the amplifier as a high-performance, general purpose
differential amplifier.
Each module front panel provides two LED indications, one for output signal limit and the other for auto-balance status.
The balance LED will light during a balance cycle, and will remain lit if an unbalanceable condition exists. It will also light
on power-up if the back-up battery is weak.
The auto-balance can be initiated for all channels with a push-button on the power supply module or with a zero-level on a
BNC located on the rear panel of the rack adapter. Also, modules can be individually auto-balanced with a recessed front
panel push-button.
Another major feature of the amplifier is that it provides two channels. One is a MAIN AC/DC channel whose parameters
are controlled from the module front panel. The other channel is a DC auxiliary channel with fixed parameters, although
the gain is jumper-selected from 1 to 500. The main channel is generally used for low-level dynamic strain measurement,
while the auxiliary channel monitors the static strain.
Detailed specifications describing the module, rack assembly and power supply are included in this manual. Also included
are outline drawings and schematics.
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Summary of Contents for 635-002
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