Strain gage amplifier with bridge completion

The AMP-SG-MH-BC is a miniature single-channel strain gage amplifier with 350 Ω completion resistors built in for quarter-bridge and half-bridge measurements. It holds a low-drift bipolar bridge excitation supply, ± 2.5 V (AMP-SG-MH-BC-5) or ± 5 V (AMP-SG-MH-BC-10), a low-noise differential amplifier and a 100 kΩ or 1 MΩ shunt calibration resistor, switched remotely in either direction. Gain is set from 100 to 2000 V/V, the output reaches ± 10 V and the response is 20 kHz at −3 dB. It runs on ± 15 V DC, measures 40.54 × 25.4 × 6.86 mm, weighs 11 g and operates from −55 to 125 °C.

Wires are soldered to the color-coded terminals, as for any electrostatic sensitive device. The amplifier is bonded with Dow Corning 3145 RTV or held by an optional metal bracket, bolted to a flat surface or fixed to a shaft with a hose clamp. Shorting the white/blue terminals gives 2000 V/V and leaving them open 100 V/V, and a resistor sets any gain between; shorting the brown terminals gives a 100 kΩ shunt and leaving them open 1 MΩ. A PS Series unit supplies ± 15 V, turns the excitation off and applies the shunt calibration.

A quarter bridge is wired in a three-wire hookup to the completion terminal, a half bridge to the bridge signal low terminal; the amplifier needs a complete bridge to regulate the excitation. Reversing the ± 15 V supplies switches the excitation off, which shows the amplifier's own offset, its noise floor and the magnetic contribution to the signal.

AMP-SG-MH-BC amplifier with its solder terminals labeled

Specifications

Channels	1
Input	Strain gage bridge (quarter or half bridge with the built-in completion resistors)
Output	Analog voltage
Output range	−10 to 10 V
Bandwidth	20 kHz (−3 dB, gain 100 and 1000)
Noise, referred to input	≤ 0.7 µV (p-p, 0.01 to 10 Hz)
Gain	100 to 2 000 V/V (100 or 2000 by jumper, any value between by external resistor)
Gain setting	Jumper · External resistor
Shunt calibration	Positive · Negative · Remote
Shunt resistor	100 · 1 000 kΩ (internal; 100 kΩ to 1 MΩ external)
Gain accuracy	≤ 0.5 % (typical: 0.05 % at gain 100, 0.50 % at gain 1000)
Gain temperature coefficient	≤ 0.0025 %/°C
Input offset	≤ 50 µV (10 µV typical)
Offset drift	≤ 0.1 µV/°C (typical, µV/°C; 1.0 µV/month)
CMRR	160 dB
Slew rate	4 V/µs
Settling time	9 µs (gain 100)
Shunt accuracy	≤ 0.1 %
Supply voltage	15 V (dual supply, ± 15 V DC)
Excitation voltage	5 to 10 V (± 2.5 V on AMP-SG-MH-BC-5, ± 5 V on AMP-SG-MH-BC-10, bipolar DC constant voltage; remote on/off)
Supply current	15 mA (per rail, plus bridge load; ± 30 mA during shunt calibration)
Excitation current limit	42 mA (84 mA on AMP-SG-MH-BC-10)
Max capacitive load	1 000 pF
Excitation accuracy	≤ 0.4 %
Excitation temperature coefficient	≤ 0.0005 %/°C
Dimensions	40.54 × 25.4 × 6.86 mm
Weight	11 g
Operating temperature	−55 to 125 °C
Compensated temperature	−25 to 85 °C
Connections	Solder terminals

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