Being phase-sensitive carrier-demodulator instruments (rather than fully DC), these models are intended for applications involving transformer coupling to the transducer bridge (as with rotary-transformer torque sensors) and for applications requiring high sensitivity with optimum signal-to-noise characteristics—as, for example, where the electrical environment is especially noisy and there is a need for high amplification of low signal levels.
The Model 3178 Strain Gage Conditioner is the basic "Form 1" instrument.
The Model 3278 Strain Gage Conditioner / Indicator is the "Form 2" instrument, providing vivid front-panel digital indication of measured values, scalable in desired engineering units.
The Model 3370 Strain Gage Conditioner / Indicator / Controller is the "Form 3" instrument, and includes HI/LO limit detection with control output.
Other important features include
- remote sensing and regulation of bridge excitation—eliminates errors from temperature effects on cable resistance
- seven-wire calibration circuitry—applies the internal shunt calibration resistor at the transducer terminals, thereby eliminating significant calibration transfer error in long-cable installations
- true differential input, with better than 80 dB of common-mode rejection—eliminates errors from common-mode pickup and possible "ground-loop" coupling
- input impedance in excess of 100 megohms preserves the validity of factory calibration, prevents conversion of common-mode to normal-mode signals, and eliminates remaining errors attributable to cable resistance. Allowable cable length has virtually no practical limits.
- elimination of both short-term and long-term drift through an advanced solid-state chopper stabilization technique, while preserving the full frequency passband, free of chopper noise; the rated accuracy is obtained without "warm-up" period or periodic "tweaking" of controls
- active low-pass filtering smooths unwanted dynamic signal components arising from vibration, power impulses, etc., that might prevent stable digital conversion or control action
3000 Series options applying to these instruments include
- Analog Peak Capture (Models 3278 and 3378)
- 4-20 mA Current Output (all models)
- 0-10 VDC Dual Galvanic Isolated Output (Models 3178 and 3278)
- Internal Relays, Electromechanical and Solid-State (Model 3378)
- 12 VDC Battery-Powered Operation (all models)
- Nominal 230 VAC Operation (all models)