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.