4
Channel Instumentation Amplifier 5312
- 5322 - 5332
Description
The 53xx series of signal conditioning modules consists of
four channel programmable gain instrumentation amplifiers with
user-selectable AC or DC input coupling, sensor voltage excitation,
input offset compensation and programmable low pass output filtering.
Optimizing the front end stage of each product offering for
a specified gain range gives cost effective signal conditioning
without sacrificing performance. The 5312 utilizes an input
attenuator for high common mode voltage applications while the
5322, and 5332, are optimized for higher gain-bandwidth applications.
Including a programmable excitation voltage source with the
ability to adjust for DC input offsets gives a complete solution
for most sensor types not requiring bridge completion.
Design Features
The 53xx series of general-purpose signal-conditioning amplifiers
utilizes onboard DSPs (one per channel) to configure the input
circuitry and handle amplifier gain and offset compensation.
A mechanical latching relay is used to select AC or DC coupling
to ensure that the input signal is not affected by the switching
circuitry. High performance front-end analog components are
combined with digital signal processing techniques and an ultra-stable
calibration reference source to maintain system accuracy. Front-panel
LEDs indicate signal presence and activity level, and warn of
module operational problems. All circuitry is housed in a shielded
enclosure for improved reliability and noise reduction.
Stable Amplifier Circuitry
After AC/DC coupling (and attenuation in Model 5312), the signal
is amplified by a fixed-gain precision instrumentation amp (x1
for 5312, 5322 or x10 for 5332). Using this approach ensures
high common-mode rejection to reduce noise pickup on the sensor
wires, and avoids the use of switched gain resistors in the
most noise and temperature sensitive portion of the circuit.
Offset adjustment is done after pre-amplification to isolate
the offset voltage generator from the sensor.
DSP - Programmable Gain
After offset correction, the signal is fed to a variable gain
amplifier controlled by an onboard DSP. A 16-bit high-speed
Sigma-Delta converter is then used to convert the amplified
signal to a digital value. Digitizing the signal for signal
processing allows all gain correction and output filtering to
be done digitally, thereby improving system accuracy. The Digital
Signal Processor uses stored offset and gain calibration factors
to correct the digitized data values and generate a digitally
filtered output that is ready for conversion back into an error-corrected
analog output voltage.
Output Circuit
The processed digital output is converted back to an analog
voltage
by a high-speed 16-bit Digital-to-Analog Converter. A four-pole
low-pass filter/buffer-amp removes the digitizing steps in the
reconstructed signal, along with any high-frequency noise. As
with the input circuit, temperature-stable components are used
to ensure that system calibration holds over a wide temperature
range.
DSP – AutoZero/AutoGain
Using a programmable offset voltage allows the DSP to automatically
servo the amplifier output to zero adjust any input offset voltage
imbalance. In a like manner, the DSP can adjust the amplifier
gain for a targeted analog output voltage value upon application
of a known calibration
signal.
Voltage Excitation with Remote Sense Capability
The 53xx provides four independent programmable excitation voltage
sources for use in powering input sensors. Each source is controlled
by a 16 bit DAC with an output range from 0 to 10 Volts and
100 mA output buffering. Remote sense can also be selected to
provide feedback accounting for IR losses over conductor lines
between amplifier and sensor.
System Calibration
High accuracy is obtained during the conversion process
by implementing a unique end-to-end calibration scheme within
the 53xx conditioner. A precision programmable voltage source
is connected to the input, and two calibration voltages (0v
and 80% of full-scale input) are fed in, amplified by the input
stages, converted by the A/D, processed by the DSP, converted
back to analog and then measured by a high-accuracy 24-bit A/D
converter. The input and output voltages are compared with the
resulting gain and offset correction values saved in the DSP
memory for real time data correction. |
Specifications
Schematic
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