Model 10A74-4C Quad Strain Gage Track-Hold Conditioner Card Datasheet

Model 10A74-4C
Quad Strain Gage Conditioner with Track-Hold

Input Type	Description	SPS6000	SPS8000	System 10
Force, Pressure, Strain, Torque, Weight	Quad Strain Gage Track-Hold	X-X	XX	XX

Intended primarily for stress analysis applications, the Model 10A74-4C receives and conditions up to four independent inputs from 1-arm (1/4-bridge), 2-arm (1/2-bridge), and 4-arm (full-bridge) strain-gage configurations attached directly to the stressed material.

To minimize possible "time-skew" effects, however, each of the four input channels has a separate track-and-hold circuit. Upon application of a "HOLD" command, the channel will instantly freeze its present value in analog memory until application of a "TRACK" command, whereupon normal tracking of the input signal is resumed. By applying a "HOLD" command simultaneously to all four channels, the user can be assured of a set of readings coherent to within a few microseconds. Unless all four inputs originate from full-bridge transducers, appropriate bridge completion is required for operation of the 10A74-4C, using any of the following:

A Model 10CJB-4 Quad Bridge Completion Card- the 10CJB-4 is identical to the Model 10CJB-2, except that it can accommodate four strain-gage inputs (rather than two)
An appropriate Daytronic Bridge Completion Connector (any version of the Model 10QBC-4 Quarter-Bridge Connector, Model 10HBC-4 Half-Bridge Connector, or Model 10FBC-4 Full-Bridge Connector)
Equivalent bridge-completion circuitry supplied by the user

The 10A74-4C provides selectable low-level excitation (1, 2, 5, or 10 V-DC). Using low excitation helps reduce gage heating effects in stress analysis of materials with low thermal conductivity. However, unlike the Model 10A72-2C, the selection of excitation level is not "per channel"; the same level applies simultaneously to all four 10A74-4C channels. Selection of the common excitation is accomplished by on-board programming jumpers only (even when a Model 10CJB-4 is connected).¹

The Model 10VAC Voltage Input Adaptor is a special screw-terminal connector assembly which allows the 10A74-4C to receive up to four independent external analog signals in place of its normal strain-gage inputs, when it is desired to apply the special TRACK/HOLD function of the 10A74-4C to these analog voltage signals.²

When a Bridge Completion Connector or Model 10VAC is not being used with the Model 10A74-4C, the card’s TRACK/HOLD function may be directly controlled through an external logic signal to its rear I/O Connector.

When the Model 10A74-4C is used in a "B-sized" System 10 mainframe (only), the TRACK/HOLD function may be alternatively controlled through an optional Model 10A1 Control Signal Card mounted in the same A-card rack. The Model 10A1 can be made to apply a continuous "HOLD" command to all 10A74-4C inputs, except during the few microseconds per scan cycle when it is itself processed as a data channel. During this processing period, the "HOLD" is released and all 10A74-4C channels are permitted to track their respective inputs. When the processing of the 10A1-dedicated channel is complete, the 10A74-4C inputs are again "held" until the next scan. A data set with minimal time-skew is thereby generated with each scan cycle.³

Any 10A74-4C strain gage channel with external bridge completion can be calibrated by either "mV/V calculated" or "shunt" calibration; the standard "two-point (deadweight)" method does not apply to such channels. "MV/V calculated" calibration of a 10A74-4C channel with external bridge completion requires entry of the nominal full-scale rating of the channel’s gage(s) in microstrain (microinches/inch), as well as the sensitivity rating in millivolts/volt.⁴ Shunt calibration provisions for the 10A74-4C are similar to those of the Model 10A72-2C, except that logic "shunt" commands to the 10A74-4C’s rear I/O Connector cannot be applied to individual channels. Such commands will affect all four channels whenever they are issued.⁵

Specifications:

Transducer Types: 1-arm (1/4-bridge), 2-arm (half-bridge), or 4-arm (full-bridge) strain gage configurations; minimum allowable gage resistance will depend on bridge excitation and gage configuration, as shown in table below; with the optional Model 10VAC Voltage Input Adaptor, the 10A74-4C can receive up to four external analog signals in place of its normal strain gage inputs
Strain Gage Transducer Ranges (full-scale, WITHOUT Model 10VAC): ±7500, 15000, or 30000 microstrain; automatically selected- on an individual channel basis- when the channel is configured
Excitation (for all four channels): Sensed excitation jumper-selectable 1, 2, 5, or 10 V-DC (i.e., ±0.5, ±1.0, ±2.5, or ±5.0 V-DC, respectively), nominal; excitation not used with optional Model 10VAC
Amplifier (per channel, WITHOUT Model 10VAC):
Analog Memory Decay Rate: Less than ±1 mV/sec⁶
Filter (per channel): 3-pole modified Butterworth; 3 dB down at 10 Hz; 60 dB down at 100 Hz
Auxiliary Outputs: Filtered outputs available on wire-wrap pins⁷

Minimum Gage Resistances for the Model 10A74-4C
Bridge Excitation	Gage Configuration	Minimum Gage Resistance
10 V-DC 10 V-DC 5 V-DC 5 V-DC 2 V-DC 2 V-DC 1 V-DC 1 V-DC	1/4 and 1/2 Bridge Full Bridge 1/4 and 1/2 Bridge Full Bridge 1/4 and 1/2 Bridge Full Bridge 1/4 and 1/2 Bridge Full Bridge	350 ohm 350 ohm* 120 ohm 350 ohm 120 ohm 60 ohm 60 ohm 60 ohm
*NOTE: When the 10A74-4C is used with four 350-ohm full-bridge transducers at 10 V-DC excitation, a special modification of the card is required to provide proper current for excitation of each bridge. Also, no more than 16 Model 10A74-4C cards using this excitation/configuration combination for all four channels can be installed in any one System 10 "A-card" rack.

Notes:

The 10CJB-4’s internal excitation selection switch does not apply to the Model 10A74-4C. (Back to Note 1)
When the 10VAC is used with the 10A74-4C, the card’s excitation level must be set to 5 V-DC. (Back to Note 2)
When linked by a special rear connector cable assembly, each 10A1 in the System 10 mainframe can communicate to each of its complement of 10A74-4C cards a TRACK/HOLD control signal received from an external computer through a Model 10A422 Communication Buffer Card in a Model 10K488 Data Concentrator (the Models 10A422 and 10K488 are fully described in the Daytronic System 10 Catalog). (Back to Note 3)
In System 10, "calculated" calibration of the 10A74-4C will use the SCALING FACTOR (EMM) command instead of the MV/V CALIBRATION (MVV) command. (Back to Note 4)
When a Model 10QBC-4, 10HBC-4, or 10FBC-4 is attached to the 10A74-4C’s rear I/O Connector, the logic-level inputs for control of shunt calibration are not available for use (in this case, shunt calibration can only be performed via software commands). (Back to Note 5)
Allows essentially perfect capture of data when used in conjunction with the Model 10A1 Control Signal Card and appropriate computer communication commands. (Back to Note 6)
Unfiltered outputs are available on special versions. Contact Daytronic for details. (Back to Note 7)

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