The single-channel Model 4077 is a versatile general-purpose instrument for input of pressure, force, torque, weight, and other variables measured by DC-excited strain gage transducers.
Unlike the other 4000 Series "Standard Input Models," the 4077 provides two special analog channels for real-time capture of both positive and negative peak input values. (ALL 4000 instruments are capable of digital peak capture, via special "MAX" and "MIN" data channels. The validity of digitally captured peak values is necessarily limited, however, by the scan rate of the instrument's Central Processor. This is not the case with the 4077's purely analog peak-capture capability, which yields true real-time maxima and minima, regardless of the current scan rate.)
The 4077 accepts a single input from any DC-excited load cell, pressure sensor, or other conventional 4-arm strain gage bridge, nominal 120 Ω or higher, with a full-scale range of 1.5 or 3.0 mV/V. Advanced circuit design overcomes many of the errors traditionally afflicting the strain gage measurement process, resulting in rock-solid digital indication and noise-free analog output.
Other important 4077 features include
- selectable bridge excitation (nominal 5 or 10 VDC)
- remote sensing and regulation of bridge excitation—eliminates errors from temperature effects on cable resistance and yields consistently stable ratiometric measurement, unaffected by possible power-supply drift
- 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.
As with most standard 4000 Series models, both active low-pass filtering and user-selectable digital smoothing eliminate dynamic components arising from vibration, power impulses, etc., that might prevent stable digital conversion or control action.
Real-Time Analog Peak Capture
The 4077's "+PEAK" channel detects and stores in capacitor memory the most positive value experienced by the input since it was last reset by an appropriate "+PEAK TRACK" command. The "-PEAK" channel detects and stores the most negative value since the last "-PEAK TRACK" command. Commands to control peak-capture operation may be issued via the Interface Port, by an optional Model 10P80D Extended Keyboard, or by TTL-level logic inputs received at the 4077's rear-panel I/O Connector.
Each peak value will remain in memory until reapplication of the respective "TRACK" command, or until occurrence of a subsequent more positive or more negative signal excursion (thus permitting the capture of successively higher maxima or successively lower minima). The following diagrams show the different possible modes of real-time peak capture (and reset); see the Model 4077 Instrument Instruction Manual for complete details.
The 4077's capacitor memory is volatile, and entails inevitable decay of captured signal values. The actual decay rate does not exceed 0.4% of full scale/second (e.g., with full scale of 20000 counts, it will not exceed 8 counts/100 msec). The decay rate is small enough to allow essentially perfect capture and indefinite (digital) hold of signal peaks, using the special digital "MAX" and "MIN" channels, as shown in the following diagram.
For a 4077-based instrument specifically dedicated to the detection, display, and evaluation of real-time peaks in all kinds of industrial applications—and offering a special "peak trend modification"—see the Model 4K/PM-77 Peak Monitor.
Simple two-point "zero and span" calibration is provided for the 4077's input channel. In addition, a 100-kΩ, 0.1% shunt resistor is supplied. You can use this resistor—or one or your own—to apply an "equivalent input" for calibration purposes, when the transducer's full-scale mV/V sensitivity is accurately known. The calibration shunt may be switched in and out for either a positive or negative up-scale reading by simple mnemonic commands issued via the Interface Port or optional Model 10P80D Extended Keyboard.
A third calibration technique for the 4077 involves application of a special MILLIVOLT/VOLT CALIBRATION (MVV) command through the Interface Port or optional keyboard when both "mV/V" sensitivity and corresponding full-scale rating of the transducer are known.
There is a special version of the Model 4077 for true, on-line Statistical Process Control (see the Model 4K/SPC-77). For a 4077-based instrument specifically dedicated to weighing operations, see the Model 4K/WT-77 Industrial Weighing Instrument.
4000 Series options applying to the Model 4077 include
- RS485 (network) data communications
- DC-powered (vehicle) operation