Frequency, Rate or Period from Pulse or AC Signals

Laureate TM Series serial output, pulse input frequency, rate and period transmitters accept two independently scalable input channels from a wide range of pulse sources, such as NPN or PNP proximity switches, contact closures, digital logic, magnetic pickups down to 12 mV, or AC voltages to 250 Vac. Input frequencies can range from 0.005 Hz to 1 MHz. Applications include AC line frequency measurement, RPM or speed from proximity switch inputs, and flow rates or totals from turbine flow meter inputs.

• With a Standard Main Board, the transmitter output can be scaled to track frequency in Hz, rate (such as gallons per minute), or period (inverse of frequency). Square root extraction is standard.
    
• With an Extended Main Board, the transmitter output can track rate or totalized rate (such as gallons) whether the transducer output is linear, requires square root extraction, or requires custom curve linearization. The latter can be provided by a curvilinear spline fit with up to 180 data points. The transmitter can also count up to a preset total or down from a preset total to zero. Such applications typically make use of optional dual solid state relays, which are available as options. External reset of totals can be via Modbus commands or via a special three-position screw terminal connector. The two input channels A & B can also be combined arithmetically to provide an analog transmitter output that tracks A+B (e.g., sum of two flows), A-B (e.g., difference of two flows), AxB (e.g., horsepower as product of force and RPM), A/B (ratio of two flow), and A/B-1 (draw or relative elongation of material between rollers).

Exceptional Accuracy and Stability at High Read Rates

Laureate pulse input frequency and rate transmitters determine frequency by taking the inverse of period as measured with a calibrated (±2 ppm) quartz crystal time base. This results in extremely accurate and stable 6-digit internal readings (±999,999 counts), which are then scaled in software to engineering units such as Hz, RPM, liters/sec, or gallons/minute. The inverse period approach provides greater accuracy and faster update times than conventional counters, which count pulses over a specified time interval. The full conversion accuracy is maintained in the Modbus output.

To reduce the effects of signal noise, a count by 10 or 100 feature with rounding is selectable. Variations in the displayed reading can also be reduced by selecting a longer gate time. An adaptive filter can reduce variations due to noise while rapidly responding to actual changes in the signal.

The update rate of the analog output is a programmed gate time + 30 ms + 0-2 signal periods. AC line frequency may be accurately measured to 50.0000 or 60.0000 Hz in a few line cycles. 1000 Hz signals may be measured to 0.01 Hz resolution at up to 25 readings per second. Fast response is ideal for alarm and control applications.

Serial Data I/O & Programming

Laureate TM Series transmitters send data as a serial digital signal. RS485 or RS232 signal levels are jumper selectable and can each be associated with either the Modbus protocol or Laurel’s simpler Custom ASCII protocol.

• Modbus protocol operation is fully compliant with the Modbus Over Serial Line Specification V1.0 (2002) for 2-wire, half-duplex connection. This includes RTU or ASCII modes, addressing of up to 32 devices per RS485 line without a repeater, and up to 247 digital addresses. Modbus operation allows devices by different manufacturers to be connected in parallel and be addressed using the same protocol.
   
• Laurel’s Laurel ASCII protocol allows up to 31 Laureate devices to be addressed on the same RS485 data line. It is simpler than the Modbus protocol and is recommended when all devices are Laureates. It also allows use of Laurel’s datalogging software.

Transmitter programming is via the unit's three-terminal serial port using Laurel's PC-based Instrument Setup Software. This software can be downloaded from this website at no charge. The required transmitter-to-PC interface cable is available from Laurel (P/N CBL03). Laurel's serial output transmitters and meters can also be part of PC-based data logging systems using Laurel's Datalogging Software, which operates under the Laurel ASCII Protocol. A single software command switches between the Modbus and Laurel ASCII Protocols.

Transmitter Options

Options include dual solid state relays for local alarm or control and an isolated 4-20 mA or 10V (selectable) analog output, effectively providing a linearized analog transmitter output that tracks the reading that would be transmitted digitally. The analog output provides 12-bit (4096 step) resolution of the output span and is ultra-linear to within one bit. Its accuracy is ±0.05% of span for all signal types, except for AC rms, where accuracy is ±0.1%. Output isolation from signal and power grounds is provided by a separate on-board power supply, which can drive 20 mA into a 500 ohm load for 10V compliance. Output isolation eliminates problems caused by ground loops.

DIN Rail Mounting 

Laureate transmitters are housed in a 35 mm DIN rail case that is only 22.5 mm (0.89") thick. Signal connections are via detachable screw clamp plug connectors.