Duty cycle is a measure of ON or OFF period as a percentage of total period. Duty cycle is determined by averaging an integral number of periods over a gate time which is selectable from 10 ms to 199.99 s. The same signal is applied to Channels A and B. The transmitter divides the average pulse width t by the period P between pulses and expresses the ratio t/P in percent. A resolution of 1%, 0.1% or 0.01% is selectable. By selecting leading or falling pulse edges, ON or OFF duty cycle can be transmitted.

Pulse Width Modulation (PWM) is a transducer output format where the measured information is provided as duty cycle applied to a constant frequeny, such as 120 Hz. As for duty cycle, the transmitter divides the average pulse width by the period between pulses over a gate time which is selectable from 10 ms to 199.99 s. It then scales this ratio mathematically to transmit this ratio in engineering units, such as relative humidity (RH).

The Laureate duty cycle & pulse width modulation transmitter uses an Extended counter transmitter main board and the FR dual-channel signal conditioner board, which accepts signals from 12 mV to 250 Vac, inputs from proximity switches with an PNP or NPN output, TTL or CMOS logic, and contact closures. Jumper selections provide optimum operation for different sensor types and noise conditions. A built-in isolated 5, 10, or 24 Vdc excitation supply can power proximity switches and other sensors.

Standard features of Laureate LT transmitters include:

• 4-20 mA, 0-10V or -10V to +10V analog transmitter output, isolated, jumper-selectable and user scalable. All selections provide 16-bit (0.0015%) resolution of output span and 0.02% output accuracy of a reading from -99,999 to +99,999 counts that is also transmitted digitally. Output isolation from signal and power grounds eliminates potential ground loop problems.
• Serial communications output, RS232 or RS485 (half or full duplex), jumper selectable. Three protocols are user selectable: Modbus RTU, Modbus ASCII, or Laurel ASCII. Modbus operation is fully compliant with Modbus Over Serial Line Specification V1.0 (2002). The Laurel ASCII protocol is simpler than the Modbus protocol and is recommended when all devices are Laureates.
• Dual solid state relays, isolated, for alarm or control. Rated 120 mA at 130 Vac or 170 Vdc.
• Transducer excitation output, isolated. User selectable 5V@100 mA, 10V@120 mA or 24V@50 mA.
• Universal 85-264 Vac power. Low-voltage 10-48 Vdc or 12-32 Vac power is optional.

Transmitter programming is via Laurel's Instrument Setup Software, which runs on a PC under MS Windows. This software can be downloaded from this website at no charge. The required transmitter-to-PC interface cable is available from Laurel (P/N CBL04).