AC Phase Angle Input Modbus or Laurel ASCII Protocol Serial I/O Transmitter

The serial output of Laureate AC phase angle transmitter indicates the lead or lag in degrees from 0º to 360º between two periodic signals having the same period. In the illustration to the left, phase angle is 360*P1/P. The signals are applied to the Channel A and B inputs of the Laureate dual-channel pulse input signal conditioner board.

Phase angle measurement is commonly used with AC power from 50 Hz to 400 Hz. Phase angle needs to be set to zero to synchronize AC generators. It also applies to the triggering of SCRs and Triacs for power control. The phase angle between AC current and voltage determines power factor. The Laureate phase angle meter and transmitter provide exceptionally fast response and high accuracy for low frequencies, such as AC line frequency.

Phase angle measurement with the Laureate phase angle meter or phase angle transmitter requires that two signals with identical periods be applied to Channels A and B. A display from -180º to +180º is obtained by timing the rising edge of one channel and the falling edge of the other channel, and programming a 180º offset. A resolution of 1º, 0.1º or 0.01º is selectable. Accuracy is 0.01% up to 100 Hz, 0.1% at 1 kHz, and 1% at 10 kHz.

Phase angle is determined by timing crystal clock pulses over a specified gate time which is selectable from 10 ms to 199.99 s. By selecting the minimum gate time of 10 ms, the update rate can be up to 20/s for 50/60 Hz AC line frequency. Improved accuracy is obtained by making the gate time long enough so that multiple cycles can be averaged.

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 I/O 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.