Model 1221
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Silicon Designs, Inc. |
Model 1221 |
| LOW NOISE SEISMIC ACCELEROMETER | ||
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• SENSOR: |
Capacitive Micromachined |
• Low
Noise: 2.0ug/(root Hz) typical
• Fully Calibrated
• Responds to DC & AC Acceleration
• ±4V
Differential Output or
.05 to 4.5V Single Ended Output
• -55
to +85 °C Operation
• +5VDC, 10mA Power
typical
• Low Current Units
Available
• ±2g Full Scale
• Integrated Sensor
& Amplifier
• LCC or J-Lead Surface Mount Package
• Serialized for
Traceability
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DESCRIPTION The Model 1221 accelerometer is a low-cost, integrated accelerometer for use in zero to medium frequency instrumentation applications that require extremely low noise. Each miniature, hermetically sealed package, combines a micromachined capacitive sense element and a custom integrated circuit that includes a sense amplifier and a differential output stage. It is relatively insensitive to temperature changes and thermal gradients. Each device is marked with a serial number in its bottom Surface for traceabilty. |
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OPERATION The Model 1221 accelerometer produces two analog output voltages which vary with acceleration as shown in the figure below. The outputs can be used either in differential or single ended modes referenced to +2.5 volts. Two reference voltages, +5.0 and +2.5 volts (nominal), are required; the output scale factor is ratio metric to the +5 volt reference voltage, and both outputs at zero acceleration are equal to the +2.5 volt reference. The sensitive axis is perpendicular to the bottom of the package, with positive acceleration defined as a force pushing on the bottom of the package. |
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SIGNAL DESCRIPTIONS
VDD and GND (Power): Pins (8,9,11,14) and (2,5,6,18,19) respectively. Power (+5 Volts DC) and ground.
AOP and AON (Output): Pins 12 and 16 respectively. Analog output voltages proportional to acceleration. The AOP voltage increases with positive acceleration, the AON voltage decreases with positive acceleration; at zero acceleration both outputs are nominally equal to the +2.5 volt reference. The device experiences positive (+1g) acceleration with its lid facing up in the earth's gravitational field. Either output can be used individually or the two outputs can be used differentially but differential measurement is recommended for both lowest noise and highest accuracy operation. Voltages can be measured ratio-metrically to VR for good accuracy without requiring a precision reference voltage. (See plot.)
DV (Input): Pin 4. Deflection Voltage. A test input that applies an electrostatic force to the sense element, simulating a positive acceleration. The nominal voltage at this pin is 1/2 VDD.
VR (Input): Pin 3. Voltage Reference. Tie directly to +5 volt power for ratio metric measurements or a +5 volt reference voltage for better absolute accuracy. A 0.1uF bypass capacitor is recommended at this pin.
2.5 Volt (Input): Pin 17. Voltage Reference. Tie to a resistive voltage divider from +5 volts or to a +2.5 volt reference voltage.
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PARAMETER |
MIN | TYP | MAX | UNITS |
| Input Range | ±2 | g | ||
| Frequency response (Nominal, 3dB) | 0-200 | 0-400 | Hz | |
| Sensitivity (Differential) 1 | 2 | Volts/g | ||
| Mechanical Shock (0.1 ms) | 2000 | g | ||
| Cross Axis Sensitivity | 2 | 3 | % | |
| Bias Calibration Error 2 | 2 | 4 | % of Span | |
| Bias Temperature Shift (TC=-55 to +85 °C) 2 | 100 | 300 | (ppm of Span)/°C | |
| Scale Factor Calibration Error 2 | 1 | 2 | % | |
| Scale Factor Temp. Shift (TC=-55 to +85 °C) 2 | +300 | ppm/°C | ||
| Output Noise (RMS) | 2.0 | ug/(root Hz) | ||
| Non-Linearity (-90 to +90% of Full Scale) 2 | 0.5 | 1.0 | % of Span | |
| Power Supply Rejection Ratio | 25 | dB | ||
| Output Impedance | 90 | Ohms | ||
| Operating Voltage | 4.75 | 5.0 | 5.25 | Volts |
| Operating Current (IDD + IVR) 3 | 10 | 14 | mA | |
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Mass: 'L' Package (add .06 grams for 'J' Package) |
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0.62 |
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grams |
Notes: 1. Single ended sensitivity is half of value shown.
2: Tighter tolerances available on special order.
3: Lower current available on special order.