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Being a phase-sensitive carrier-demodulator instrument (rather than fully DC), the Model 3578 is 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.

Responding only to the modulated carrier frequency, the 3578 rejects extraneous voltages that can cause errors in DC systems.  Excitation is fixed at 3 VAC (rms) at 3280 Hz.

Other important 3578 features include

	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
	high input impedance 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.
	user-settable phase and symmetry controls for accurate calibration
	selectable active low-pass filtering smoothes unwanted dynamic signal components arising from vibration, power impulses, etc., that might prevent stable digital conversion or control action (see Specifications)

Simple two-point "zero and span" calibration is provided for the 3578's input channel.  In addition, a 100-kΩ, 0.1% shunt resistor is supplied.  You can use this resistor—or one of 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 via simple commands issued to the RS232/RS485 port.

[NOTE: Unlike the Model 3570 DC Strain Gage Conditioner, the 3578 employs a special Conditioner Connector, which requires direct solder-terminal attachment of cable leads, and does not permit the input of logic-level signals for control of shunt calibration.  Also the Model 3578 cannot be calibrated by means of the software MVV command.]

The 3578 offers all standard 3500 Series features, including

	selectable digital smoothing
	custom 15-segment linearization
	HI/LO limit monitoring with logic I/O
	scalable analog output
	analog +peak capture
	automatic tare offset
	digital track and hold
	either single-node (RS232) or multinode network (RS485) communications

The instrument can be completely set up and operated either through the front-panel keypad or via simple mnemonic commands received from an external computer or terminal through the RS232/RS485 Interface Port.

For a typical 3578 operation, see the following application:

Bearing Friction Testing

AC Strain Gage Conditioner Specifications  [Top ] (Click here for 3500 Series General Specifications; see also the statement on Daytronic accuracy specifications)
Input Type	Conventional 4-arm strain gage bridge, nominal 90 Ω or higher
Input Ranges (full-scale)*
Nominal Input Range Actual Normal-Mode Input-Signal Voltage (Max.) Absolute Maximum Overrange (50%) Input at which Display Reading Corrsponds to "m" Term 3.00 mV/V 13.5 mV/V 4.0 mV/V 4.0 mV/V 1.50 mV/V 6.75 mV/V 2.0 mV/V 2.0 mV/V 0.75 mV/V 3.375 mV/V 1.0 mV/V 1.0 mV/V
Excitation Supplied	Regulated 3 VAC (rms) at 3280 Hz; 50 mA (rms) maximum
Amplifier	AC-coupled demodulator with user-settable phase and symmetry controls
Normal-Mode Range	±12 mV-AC (rms) operating; ±8 VDC without instrument damage
Common-Mode Range	±0.8 VDC operating; ±8 VDC without instrument damage
Common-Mode Rejection Ratio	Infinite at DC; -90 dB at 60 Hz; -80 dB at 1 kHz; -60 dB at 3 kHz
Input Impedance (Differential and Common-Mode)	10 MΩ
Offset	Initial: ±3% of full scale Vs. Temperature: ±0.005% of full scale/°C Vs. Time: ±0.002% of full scale/month
Gain Accuracy	±0.025% of full scale ± 1 count LSD, typical, following calibration**
Gain Stability	Vs. Temperature: ±50 ppm/°C Vs. Time: ±20 ppm/month
Analog Filtering
Fixed	20 Hz
Selectable	5-pole filter with selectable low-pass corner frequency of 5, 10, or 20 Hz
Frequency Characteristics	Corner Frequency   Response at . . . 5 Hz 10 Hz 20 Hz -3 dB 5 Hz 10 Hz 20 Hz -60 dB 32 Hz 65 Hz 125 Hz
Step Response Settling Time (Full-Scale Output)	Corner Frequency    5 Hz 10 Hz 20 Hz To 1% of final value 250 ms 125 ms 100 ms To 0.1% of final value 400 ms 200 ms 150 ms To 0.02% of final value 600 ms 300 ms 225 ms
Peak Capture	Positive analog peak, digitally held for indefinite display; minimum full-scale input pulse duration is 100 msec (to 1% of full-scale accuracy), 150 msec (to 0.1% of full scale accuracy), and 225 msec (to 0.02% of full-scale accuracy); PEAK and TRACK modes controlled by front-panel button, rear-panel logic input, or computer-port command
Analog Output***: See 3500 Series General Specifications
Frequency Characteristics and Step Response Settling Times	After (A) FIXED ANALOG FILTER and after (B) +PEAK in "PEAK" or "TRACK" Mode: -3 dB at 20 Hz; -60 dB at 250 Hz; settling time to 1% of final value: 100 msec; to 0.1% of final value: 150 msec; to 0.02% of final value: 225 msec After (C) SELECTABLE ANALOG FILTER: See Analog Filtering (Selectable), above
* Since channel zeroing is by digital techniques, no input balance control is provided.  The allowable input range, therefore, must include an initial unbalance (which, in commercially produced strain gage transducers, is negligible).  Other transducers may have to be externally trimmed to be used with the Model 3570, if zero unbalance exceeds 20% of full scale. ** Initial (uncalibrated) inaccuracy may be as great as ±3% of full scale.  Maximum error that could occur upon replacement of the Model 3578 not followed by calibration is ±6% of full scale. *** When the analog output scale is 100.0% and the analog output offset is 0.0%, then any of the following inputs will result in an analog output of 5 V: an input of 4 mV/V on the 3.0-mV/V range; an input of 2 mV/V on the 1.5-mV/V range; or an input of 1 mV/V on the 0.75-mV/V range.