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The Model 3540 is used for measurement of flow, rpm, and other phenomena that can be sensed by pulse transformer transducers with two-wire isolated windings (tachometer pickups, turbine flowmeters, etc.), transistor or logic-circuit drivers, "zero-velocity" (true digital output) sensors, and similar frequency-generating transducers.  It will accept virtually any AC or unipolar pulse input signal, floating or grounded.

The 3540's analog-input threshold level is selectable to accommodate signals from 100 mV to 100 V, thus guaranteeing reliable triggering when the input is at the low end of the frequency range.  Capacitive coupling of 0.1 μF is provided for low-frequency inputs, to eliminate false triggering by signal noise or any DC offset that exists for the frequency signal.  For "zero-velocity" sensors, ±5 VDC excitation is supplied.

When you know the manufacturer-supplied full-scale rating of the frequency source (or the highest frequency expected to be measured), the Model 3540's measurement channel can be quickly and easily calibrated by issuing the special FREQUENCY CALIBRATION (FRQ) command through the RS232/RS485 Interface Port.

With the exception of analog peak capture, the 3540 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
	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 typical 3540 operations, see the following applications:

	Flow Indication
	Measuring Motor RPM

Frequency Conditioner Specifications  [Top ] (Click here for 3500 Series General Specifications; see also the statement on Daytronic accuracy specifications)
Input Type	Any AC or unipolar pulse signal, grounded or floating, irrespective of waveform
Frequency Range	From 10% to 100% of 250, 500, 1000, 2000, 4000, 8000, 16000, or 32000 Hz
Threshold Level	Selectable to accommodate signals from 100 mV to 100 V
Excitation Supplied (for "Zero-Velocity" sensors)	Nominal ±5 VDC ± 5%; ±50 mA maximum
Normal-Mode Range	±100 V operating; ±150 V without instrument damage
Common-Mode Range	±100 V operating and without instrument damage
Common-Mode Rejection Ratio	-120 dB at 60 Hz; -60 dB at 1 kHz
Input Impedance	Normal-Mode: 200 kΩ Common-Mode: 50 kΩ
Offset	Initial: ±0.05% of full scale Vs. Temperature: ±25 ppm/°C Vs. Time: ±20 ppm/month
Gain Accuracy	±0.02% of full scale ± 1 count LSD
Gain Stability	Vs. Temperature: ±40 ppm/°C Vs. Time: ±20 ppm/month
Analog Filtering
Selectable Filter	5-pole filter with selectable low-pass corner frequency of 2.5, 5, or 10 Hz
Frequency Characteristics	Corner Frequency   Response at . . . 2.5 Hz 5 Hz 10 Hz -3 dB 2.5 Hz 5 Hz 10 Hz -60 dB 15 Hz 32 Hz 65 Hz
Step Response Settling Time (Full-Scale Output)	Corner Frequency    2.5 Hz 5 Hz 10 Hz To 1% of final value 450 ms 275 ms 150 ms To 0.1% of final value 850 ms 425 ms 225 ms To 0.02% of final value 1.3 s 650 ms 350 ms
Peak Capture (Digital)	Displays the most positive measurement reading, which is digitally held for indefinite display; 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	See Analog Filtering, above