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Model 10A78
 AC Strain Gage Conditioner

Input Type Description SPS6000 SPS8000 System 10
Force, Pressure, Strain,
Torque, Weight 		AC Strain Gage X*X
 X-X
 X*X


This card is similar to the Model 10A70-2, but is a single-channel conditioner of phase-sensitive carrier-amplifier design (rather than a two-channel, fully DC instrument). Intended for applications involving transformer-coupling to the transducer bridge (as with rotary-transformer torque sensors), it can also be used when high sensitivity is required or where the electrical environment is especially noisy. Responding only to the modulated carrier frequency, the 10A78 rejects extraneous voltages that can cause errors in DC systems, particularly when there is a need to "blow up" a portion of the transducer range.

Regardless of the system in which it is used, the Model 10A78's data channel can be calibrated by means of a "two-point" ("deadweight") or shunt-calibration technique (see the Model 10A72-2C), following an initial phase and symmetry adjustment. The supplied calibration resistor is 59 kilohms, 1%. A specially modified version of the 10A78 is required if you wish to control the shunt-calibration process by means of logic-level inputs through the rear I/O Connector.

In the SPS6000 System (only), "calculated" calibration can also be applied to the 10A78, when both "mV/V" sensitivity and the corresponding full-scale rating of the transducer are known. Unlike the Models 10A70-2 and 10A72-2C, the 10A78 can not be calibrated via the System 10 MV/V CALIBRATION (MVV) command.

Specifications:
  • Transducer Types: Conventional 4-arm strain gage bridges, nominal 350 ohm or higher
  • Input Ranges (full-scale): ±0.75, 1.50, or 3.00 mV/V; automatically selected- on an individual channel basis- when the channel is configured; user-adjustable phase and symmetry controls are provided*
  • Excitation: Regulated 3 V-AC (rms) at 3280 Hz; 50 mA (rms), maximum
  • Amplifier:
      Common-Mode Range: ±1 V operating; ±9 V without instrument damage
      Common-Mode Rejection Ratio: DC and at 60 Hz: infinite; at 3 kHz: -60 dB
      Input Impedance (Differential and Common-Mode): 10 M-ohm
      Offset: Initial: ±3% of full scale; vs. Temperature: ±0.005% f.s./°C; vs. Time: ±0.02% f.s./month
      Gain Accuracy: ±0.02% of full scale typical, following calibration**
      Gain Stability: vs. Temperature: ±50 ppm/°C; vs. Time: ±20 ppm/month
  • Filter: 3-pole modified Butterworth; 3 dB down at 7.5 Hz; 60 dB down at 60 Hz
      Step-Response Settling Time (Full-Scale Output):
      To 1% of final value: 250 msec
      To 0.1% of final value: 350 msec
      To 0.02% of final value: 500 msec
  • Auxiliary Output: Filtered output available on wire-wrap pin
    *Since channel zeroing is by digital techniques, no input balance control is provided. The allowable input range, therefore, must include any initial unbalance (which, in commercially produced strain gage transducers, is negligible). Other transducers may have to be externally trimmed to be used with the Model 10A78, if zero unbalance exceeds 20% of full scale.
    **Initial (uncalibrated) inaccuracy may be as great as ±3% of full scale (see Accuracy Specifications). Maximum error that could occur upon replacement of a Model 10A78 not followed by calibration is ±6% of full scale.


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