Measurements Group Strain Gauge Instrumentation

Model 3800 Wide Range Strain Indicator 

Gauge factor on the Model 3800 is settable by front panel controls over a range of 0.0500 to 50.00, and is displayed by the LED readout when in the SET position. The instrument allows full range display (+19 999 counts) over the complete gauge factor range.

Excitation voltage is precisely settable over a range of 1-15 volts in 1-volt increments by a front-panel thumb-wheel switch. The output display automatically tracks the excitation setting so that gauge factor does not vary with bridge voltage.

The balance system in the Model 3800 has four ranges which are selected by the BALANCE RANGE push buttons. Each range is further divided into four sub-ranges by the COARSE balance switch. The FINE balance control provides an additional adjustment range that overlaps the COARSE balance switch positions. This unique system provides a total of 32 overlapping ranges for achieving precise balance settings and resolution. All balance voltages are electronically injected into the input amplifier to eliminate bridge loading errors and preserve full measurement range.

Input circuitry includes an ultra-stable internal half-bridge, as well as internal 120, 350, and 1000 ohm dummy gauges for bridge completion. Shunt calibration resistors across the internal dummy gauges are provided on the rear panel. Two remote calibration resistors, also mounted on the rear panel, are automatically actuated by the front panel calibration button.

Virtually all strain-gauge-based transducers can be used with the Model 3800 via the rear-panel transducer connector. This connector provides precision remote-sense capability, as well as access to the remote calibration resistors. Full-scale resolutions of 0.10 microvolt/volt are routinely possible. By using the wide-range balance controls to suppress zero, resolutions to 0.025 microvolt/volt can be achieved.

In addition to the digital LED display, the Model 3800 provides an analogue output available at the rear panel. A separate analogue level control totally independent of the digital display is also provided.

The Model 3800 Wide Range Strain Indicator is an exceptional, high-resolution instrument that will make a valuable contribution to any experimental stress analysis or transducer development laboratory. 

Features

• 4-1/2 Digit LED Display 

• ANSI/SEM Colour-Coded Bridge Connection Terminals 

• Analogue Output 

• Transducer Connector with Remote Sense 

• Manual, Direct Reading of Strain, Pressure, Torque, Load, and other Engineering Variables 

• Convenient Colour-Coded Push-Button Controls 

• Gauge Factor Range from 0.0500 to 50.00 Displayed on LED Readout (to four significant digits) 

• Bridge Excitation Range from 1.000 to 15.000 Vdc, DC Step Selectable 

• Extremely Wide Balance Range, High-Precision Laboratory Strain Indicator. Balance by Voltage Injection. 

• Quarter-, Half-, and Full-Bridge Circuits 

• Separate Bridge Excitation On/Off Control 

• Built-in 120/1000 and 350 ohm Dummy Gauges

Specifications
All specifications nominal or typical at +23 deg C unless noted.
Throughout these specifications, RTI is used as an acronym for "referred to input".

Range
++19 999 counts direct-reading LED display.

Resolution
+1 microstrain at any Gauge Factor from 0.500 to 50.00
0.10 microvolt/volt as a transducer indicator.

Linearity
+0.1% of full scale.

Balance Range
Coarse Balance: +2.5% to +100% of full scale per step, in 32 total steps.
Fine Balance: +1.25% to +50% of full scale; overlaps each coarse balance step.

Balance Method
Electronically injected counter-emf.

Gauge Factor
Range: 0.0500 to 50.00; displayed by LED readout when in the SET position.
Resolution: 
0.0001 from GF of 0.0500 to 0.5000.
0.001 from GF of 0.500 to 5.000.
0.01 from GF of 5.00 to 50.00.

Linearity: +0.05% of full scale.
Accuracy: +l least significant digit.

Excitation Voltage
1.000 to 15.000 Vdc +1 mV +0.02%. Settable in 1V increments by front-panel thumbwheel switch.
Temperature Stability: +0.01%/deg C.

Amplifier
Temperature Effect on Zero: 
+1.0 microvolt/deg C RTI max.;
+0.50, microvolt/deg C RTI typical. 
Temperature Effect on Span: +0.005%/deg C max.
Warm-up Drift: Less than +3 microvolt RTI from turn-on to 5 minutes.
Random Drift at Constant Ambient Temperature: Less than +1 microvolt RTI.
Common-Mode Rejection: Greater than 100 dB at 50-60 Hz.
Common-Mode Voltage: +8V max.
Input Impedance: Greater than 100 megohms differential and common mode.
Input Circuits: Quarter-, half-, and full-bridge circuits. Internal bridge completion provided for 120/1000 ohm and 350 ohm quarter bridges; 60 to 2000 ohm half- or full-bridge.
Calibration: Shunt calibration resistors are provided across internal 120-ohm and 350-ohm dummy gauges to simulate 5000 microstrain +0.05%. Calibration resistors are located on the rear of instrument and may be changed to suit specific requirements.
Contact closures are provided for two rear-panel mounted resistors to facilitate any calibration configuration. Typical use is double-shunt calibration of transducers.

Analogue Output
Linear Output: +10.00 volt max; adjustable over 11:1 range by a ten-turn potentiometer mounted on the rear panel.
Output Load: 2000 ohms min.
Bandwidth: 
GF > 0.500, DC to 4.5 kHz (-3 dB nominal).
GF < 0.500, DC to 2.0 kHz (-3 dB nominal). 
Output Noise: Less than 2.5 microvolts peak to peak 0.10 to 10 Hz, RTI. Less than 2 microvolts rms dc to 5 kHz, RTI, plus 0.005% of full scale, RTO (referred to output).

Remote Sense
Remote sense connections provided at transducer connector.
Remote Sense Error: Less than 0.0005%/ohm of lead resistance. Maximum lead resistance 40 ohms or less.

Power
115/230 Vac, 50-60 Hz, less than 10 volt-amperes.

Size & Weight
6.5 H x 11.0 W x 12.5 D in (165 x 280 x 318 mm).
10.2 lb (4.6 kg).