SRS Labs SR785 Specifications, Measurement Groups, Frequency, Dynamic Range, Phase Accuracy

SR785 Specifications

Specifications apply after 30 minutes of warm-up and within two hours of last auto-offset. All specifications are with 400 line FFT resolution and anti-alias filters enabled unless stated otherwise.

Measurement Groups

Standard Groups	FFT analysis, Correlation, Time
	Histogram, Swept Sine
Optional Group	Order Tracking

Frequency

Range	102.4 kHz or 100 kHz (both displays
	have the same range).
FFT Spans	195.3 mHz to 102.4 kHz or 191 mHz to
	100 kHz. The two displays can have
	different spans and start frequencies.
FFT Resolution	100, 200, 400 or 800 lines
Real-Time Bandwidth	102.4 kHz (highest FFT span with con-
	tinuous data acquisition and averaging).
Accuracy	25 ppm from 20 ˚C to 40 ˚C

Dynamic Range

Dynamic Range	-90 dBfs typical, -80 dBfs guaranteed
	(FFT and Octave)
	-145 dBfs typical (Swept-Sine)
	Includes spurs, harmonics, intermodu-
	lation distortion and alias products.
	Excludes alias responses at extremes of
	span.
Harmonic Distortion	<-80 dB (single tone in band)
Intermod. Distortion	<-80 dB (two tones in band, each
	less than -6.02 dBfs)
Spurious	<-80 dBfs
Alias Responses	<-80 dBfs (single tone outside of span,
	less than 0 dBfs, less than 1 MHz)
Full Span FFT Noise	100 dBfs typical (input grounded, input
Floor	range >-30 dBV, Hanning window,
	64 RMS averages)
Residual DC Response	<-30 dBfs (FFT with Auto Cal on)

Amplitude Accuracy

Single Channel	±0.2 dB (excluding window effects)
Cross Channel	±0.05 dB (dc to 102.4 kHz)
	(frequency response measurement, both
	inputs on the same input range, RMS
	averaged)

Phase Accuracy

Single Channel	±3.0 deg relative to External TTL
	trigger (-50 dBfs to 0 dBfs, freq
	<10.24 kHz, center of frequency bin,
	DC coupled). For Blackman-Harris,
	Hanning, Flattop and Kaiser windows,
	phase is relative to a cosine wave at the
	center of the time record. For Uniform,
	Force and Exponential windows, phase
	is relative to a cosine wave at the
	beginning of the time record.

Cross Channel	±0.5 deg (dc to 51.2 kHz)
	±1.0 deg (dc to 102.4 kHz)
	(frequency response measurement, both
	inputs on the same input range, vector
	averaged)

Signal Inputs

Number of Inputs	2
Full Scale Input Range	-50 dBV (3.16 mVpk) to +34 dBV
	(50 Vpk) in 2 dB steps
Maximum Input Level	57 Vpk
Input Configuration	Single-ended (A) or true differential
	(A-B)
Input Impedance	1 MΩ + 50 pF
Shield to Chassis	Floating mode: 1 MΩ + 0.01 mF
	Grounded mode: 50 Ω
	Shields are always grounded in
	differential input (A-B)
Maximum Shield Voltage 4 Vpk
AC Coupling	-3 dB rolloff at 0.16 Hz
CMRR	90 dB at 1 kHz (in. range <0 dBV)
	80 dB at 1 kHz (in. range <10 dBV)
	50 dB at 1 kHz (in. range ≥ 10 dBV)
ICP Signal Conditioning	Current Source: 4.8 mA
	Open Circuit Voltage: +26 V
A-Weight Filter	Type 0 Tolerance, ANSI Standard
	S1.4-1983; 10 Hz to 25.6 kHz
Crosstalk	<-145 dB below signal (input to input
	and source to inputs, 50 Ω receiving
	input source impedance)
Input Noise	<10 nVrms/√ Hz (<-160 dBVrms/√ Hz)
	above 200 Hz

Trigger Input

Modes	Free run, Internal, External, or External
	TTL
Internal	Level adjustable to ±100% of input
	scale, positive or negative slope.
	Minimum Trigger Amplitude: 5% of
	input range
External	Level adjustable to ±5 V in 40 mV
	steps, positive or negative slope.
	Input impedance: 1 MΩ
	Max input: ±5 V
	Minimum trigger amplitude: 100 mV
External TTL	Requires TTL level to trigger
	(low <0.7 V, high >3.0 V)
Post-Trigger	Measurement record is delayed up to
	100,000 samples after the trigger.
Pre-Trigger	Measurement record starts up to 8000
	samples prior to the trigger.

Tachometer Input

Pulses Per Revolution	1 to 2048
RPM Accuracy	±50 ppm (typical)
Tach Level Range	±25 V, ±5V, TTL
Tach Level Resolution	20 mV @ ±25 V, 4 mV @ ±5 V
Max. Tach Input Level	±40 Vpk
Min. Tach Pulse Width	100 nSec
Max. Tach Pulse Rate	750 kHz (typical)