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Model AA72
 Enhanced Strain Gage Conditioner

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


Model AA72 Strain Gage Conditioning Card Image The AA72 is a general-purpose 2- or 4-channel conditioner for input of pressure, force, torque, weight, and other variables that may be measured by conventional DC-excited load cells, pressure sensors, and other strain gage transducers employing a four-arm bridge of nominal 350 ohm or higher. Like the "10A" Strain Gage Conditioners, the AA72 is based on a reliable amplifier-per-channel design with solid-state chopper stabilization, and features

AA72 I/O connector, shown open
  • selectable per-channel excitation using remote sensing of bridge voltage and slaved to a common System Reference Voltage
  • input impedances in excess of 10,000 M-ohm
  • per-channel shunt calibration resistors (for the AA72, these are 100-K-ohm, 0.1% and are easily accessible from the rear I/O Connector assembly). As with the 10A72-2C, the AA72’s shunt resistors may be switched in and out by software, or by means of logic-level inputs through the rear I/O connector.


Standard "AA"-card features of the AA72- including programmable low-pass active filtering- are described on the Overveiw of "AA"-cards page.

Model AA72 data channels may be accurately calibrated in several ways:
  through a conventional "two-point" ("deadweight") procedure
  by a convenient "calculated" calibration technique, when both "mV/V" sensitivity and the corresponding full-scale rating of the transducer are known
  by means of the shunt calibration resistors mentioned above, when overall "deadweight" and/or "mV/V-computed" calibration is impractical


Specifications:
  • Number of Input Channels: Two or four (specify AA72-2 or AA72-4, respectively)
  • Transducer Types: Conventional 4-arm strain gage bridges, nominal 350 ohm or higher; 1/4- and 1/2-bridge gage configurations can be accommodated by means of the Model 10CJB-2 Dual Bridge Completion Card or equivalent external bridge-completion circuitry supplied by the user
  • Input Ranges (full-scale): See table below; automatically selected- on an individual channel basis- when the channel is configured*
  • Excitation (per channel): Jumper-selectable 1, 5, or 10 V-DC (i.e., ±0.5, ±2.5, or ±5 V-DC, respectively), nominal; ±40 mA, maximum, for each voltage, subject to 120 mA total current draw for all 4 channels**
  • Amplifier (per channel):
      Normal-Mode Range: ±40 mV operating (±3.6 mV/V with 10-V exci-tation); ±8 V without instrument damage
      Common-Mode Range: ±1 V operating; ±8 V without instrument damage
      Common-Mode Rejection Ratio: DC and at 60 Hz: -120 dB
      Input Impedance (Differential and Common-Mode): Greater than 10,000 M-ohm
      Offset: Initial: ±0.02 mV; vs. Temperature: ±1 µV/°C; vs. Time: ±5 µV/month
      Gain Accuracy: ±0.02% of full scale
      Gain Stability: vs. Temperature: ±50 ppm/°C; vs. Time: ±20 ppm/month
  • Filter (per channel): Programmable or fixed; see AA Card Features, Tables 1 and 2
  • Auxiliary Outputs: Nominal ±5 V-DC signals available on wire-wrap pins; individually jumper-selectable to represent either the filtered or pre-filtered (5-kHz bandwidth) reading of the channel
  • Power-Supply Slot Allotment: This card has the potential of consuming 200 mA of supply current from the Conditioner Card Slot (the actual consumption for any given channel will depend on its transducer bridge resistance and excitation level)
    *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 AA72, if zero unbalance exceeds 20% of full scale.
    **For this reason, 10-V excitation should not be used with transducer bridges of 120-ohm or lower.

Strain Gage Ranges for the Model AA72
1-V Excitation
5-V Excitation
10-V Excitation
7.5 mV/V
15.0 mV/V
30.0 mV/V
 1.5 mV/V
3.0 mV/V
6.0 mV/V
 0.75 mV/V
1.50 mV/V
3.00 mV/V



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