4-20 mA & RS485 Output Transmitter for Duty Cycle or Pulse Width Modulation (PWM) Input

Transmits duty cycle in percent or pulse width modulated input signals in engineering units. DIN rail mounted, digitally programmable.

Duty cycle transmitter

Standard Features

  • 4-20 mA, 0-20 mA, 0-10V or -10V to +10V transmitter output, 16 bits, isolated
  • RS232 or RS485 serial data output, Modbus or TDM ASCII protocol, isolated
  • Dual 120 mA solid state relays for alarm or control, isolated
  • Transmits duty cycle with resolution of 1%, 0.1% or 0.01%.
  • Transmits pulse width modulated (PWM) signal inputs in engineering units
  • Frequencies from 0.005 Hz to 10 kHz
  • Inputs from NPN or PNP proximity switches, contact closures, digital logic, magnetic pickups down to 12 mV, or AC inputs up to 250 Vac.
  • Analog output resolution 0.0015% of span (16 bits), accuracy ±0.02% of span
  • 5V, 10V or 24V dc transducer excitation output, isolated
  • Universal 85-264 Vac / 90-300 Vdc or 10-48 Vdc / 12-32 Vac power
  • Custom curve linearization and rate from successive readings (optional)
Clock diagram, 4-20 mA duty cycle transmitter

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).

RTD signal conditioner board

The 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 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 TDM ASCII. Modbus operation is fully compliant with Modbus Over Serial Line Specification V1.0 (2002). The TDM ASCII protocol is simpler than the Modbus protocol and is recommended when all devices are s.
  • 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 TDM'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 TDM (P/N CBL04).

Duty Cycle Measurement
Item Transmitted ON or OFF duty cycle of periodic pulse waveshape
Displayed Units 1%, 0.1%, 0.01%
Frequency Range 0.005 Hz to 10 kHz
Accuracy 0.01%, 0.005 Hz to 500 Hz, 0.1% at 5 kHz, 1% at 10 kHz
Maximum Timing Interval 199.99 s
Pulse Width Modulation (PWM) Measurement
Item Transmitted Measurement based on Pulse Width Modulation (PWM) input
Displayed Units Scaled reading in engineering units
Frequency Range 0.005 Hz to 10 kHz
Accuracy 0.01%, 0.005 Hz to 500 Hz, 0.1% at 5 kHz, 1% at 10 kHz
Maximum Timing Interval 199.99 s
Update Rate
Conversion Interval Gate time + 30 ms + 0-2 signal periods
Gate Time Selectable 10 ms to 199.99 s
Time Before Zero Output Selectable 10 ms to 199.99 s
Pulse Input
Types AC, pulses from NPN, PNP transistors, contact closures, magnetic pickups
Grounding Common ground for channels A & B.
Minimum Signal Nine ranges from (-12 to +12 mV) to (+1.25 to +2.1V)
Maximum Signal 250 Vac
Noise Filter 1 MHz, 30 kHz, 250 Hz (selectable)
Contact Debounce 0, 3, 50 ms (selectable)
Analog Output (standard)
Output Levels 4-20 mA, 0-20 mA, 0-10 Vdc, -10 to +10Vdc (user selectable)
Compliance at 20 mA 10V (0-500Ω load)
Compliance at 10V 2 mA (5 kΩ load)
Output Resolution 16 bits (65,536 steps)
Output Accuracy 0.02% of output span plus conversion accuracy
Output Isolation 250V rms working, 2.3 kV rms per 1 minute test
Serial Data Output (standard)
Signal Types RS232 or RS485 (half or full duplex), jumper selectable
Data Rates 300, 600, 1200, 2400, 4800, 9600, 19200 baud
Output Isolation 250V rms working, 2.3 kV rms per 1 min test
Serial Protocols Modbus RTU, Modbus ASCII, TDM ASCII
Modbus Compliance Modbus over Serial Line Specification V1.0 (2002)
Ethernet Connector RJ45 jack for 10/100 Base-T Ethernet cable
RS232/RS485 Connector Screw terminals for easy daisy chaining
Digital Addresses 247 for Modbus, 31 for TDM ASCII
Dual Relay Output (standard)
Relay Type Two solid state relays, SPST, normally open, Form A
Load Rating 120 mA at 140 Vac or 180 Vdc
Sensor Excitation Output (standard)
Output Levels 5V@100 mA, 10V@120 mA, 24V@50 mA (jumper selectable)
Output Isolation 50V from signal ground
Power Input
Standard Power 85-264 Vac or 90-300 Vdc
Low Power Option 10-48 Vdc or 12-32 Vac
Power Frequency DC or 47-63 Hz
Power Isolation 250V rms working, 2.3 kV rms per 1 min test
Power Consumption 2W typical, 3W with max excitation output
Dimensions 129 x 104 x 22.5 mm case
Mounting 35 mm rail per DIN EN 50022
Electrical Connections Plug-in screw-clamp connectors
Operating Temperature 0°C to 55°C
Storage Temperature -40°C to 85°C
Relative Humidity 95% at 40°C, non-condensing
Cooling Required Mount transmitters with ventilation holes at top and bottom. Leave 6 mm (1/4") between transmitters, or force air with a fan.
 LT transmitter pinout
Applications Example
Duty Cycle & Pulse Width Modulation (PWM) Modes
Duty cycle graph In duty cycle mode, the transmitter displays ON or OFF time in percent from 0% to 100% of period for repetitive pulse trains. In the illustration, duty cycle in percent is 100 x t/P.

In pulse width modulation (PWM) mode, the meter also determines the duty cycle ratio, but then scales this ratio for display in engineering units.

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