Model 70A is a full featured, wideband differential instrumentation amplifier which can be used for a variety
of applications. Designed to condition, amplify and filter low level analog signals it is used for data
acquisition, analog recording, line and galvanometer driving, data filtering and signal isolation.
The basic element is a very stable, low noise differential amplifier with wideband response. Input impedance
is 50 Megohms, linearity is 0.01% and common mode rejection is 130 dB for up to 300 Volts. Bandwidth exceeds
100 kHz for gains from 1 to 1,000.
Eleven switch selectable gains and a variable gain multiplier provide continuous coverage from 1 to 5,000. An
optional attenuator extends the gain range from 0.01 to 5,000. Gain accuracy is ±0.1% with ±0.01% available
as an option. The 70A-5 has a two pole, switch selectable, low pass filter with Bessel response. The 70A-6
is the same, but with six pole Bessel response. Butterworth response is also available.
Model 70A provides two independently buffered ±10 Volt full scale outputs each with 100 milliampere drive
current. Output impedance is less than 0. 1 Ohm for driving long lines and capacitive loads. Output is short
circuit protected and current is limited to safeguard external equipment.
Each amplifier is floating and line powered providing channel to channel isolation. It is fully enclosed in a
metal case and mechanically secured when installed in the enclosure. Ten amplifiers mount in a 5¼ inch high rack
enclosure with a rear mounted connector panel.
Specifications - Model 70A
Input
Two wire with shield. Withstands ±50 Volts differential and ±350 Volts common mode without damage.
Input Impedance
50 Megohms shunted by 100 pF
Calibration
Amplifier input is switched to calibration bus by a guarded low-level relay. Activated by TTL control input
Gain
Eleven switch selectable gains of 1, 2, 5, 10, 20,50,100,200,500, 1000 and 2000 with ±0.1% accuracy (±0.01% optional).
Variable gain multiplier increases step gain covering range of 1 to 5,000. Stability is ±0.01%, ±0.002%/¡C.
Linearity
±0.01 %
Zero Stability
±5 µV RTI, ±0.5 mV RTO. Temperature coefficient is ±0.4 µV/°C RTI, ±0.15 mV/¡C RTO
Common Mode
130 dB at DC, 123 dB at 60 Hz for gain 1000, and 1 K Ohm source unbalance. Operating common mode voltage is ±300 Volts DC or peak AC.
Bandwidth
100 kHz.
Filter (70A-5)
Switch selectable, 12 dB/octave Bessel low pass with 3 dB bandwidth steps of 1 Hz, 10 Hz, 100 Hz, 1 kHz, 10 kHz and Wideband.
Butterworth response is available.
Filter (70A-6)
Switch selectable, 36 dB/octave Bessel low pass with 3 dB bandwidth steps of 1 Hz, 10 Hz, 100 Hz, 1 kHz, 10 kHz and Wideband.
Butterworth response is available.
Gains from 0.01 to 5,000
