Modbus & Serial Output Transmitter for
Position or Rate from Quadrature Encoders

 
Standard Features

• Accepts low-level differential or single-ended 5V logic level outputs from a shaft encoder, linear encoder, incremental encoder or optical encoder.
• Isolate serial data output with selectable Modbus or Micron ASCII protocol
• Modbus RTU or ASCII modes, 2-wire connection, up to 247 digital addresses
• Programmable for position, angle or rate
• Quadrature count x1, x2 or x4
• Combined pulse rate to 250 kHz
• Display refresh rate up to 25/s
• Zero channel input
• DIN rail mount package only 22.5 mm thick
• Detachable screw clamp plug connectors
• Easy setup with PC-based Instrument Setup Software
• 5V, 10V or 24V dc sensor excitation output, isolated
• Dual solid state relays for alarm or control, isolated
• 0-10V, 4-20 mA or 0-20 mA analog output, scalable, isolated
• Universal AC power, 85-264 Vac
• Priced Reasonably (basic quadrature transmitter)
  Options:
• Low voltage power, 10-48 Vdc or 12-30 Vac

Description

The Micron Modbus & serial output, quadrature input transmitter accepts the A & B quadrature encoder signals to provide an analog output that tracks that tracks position, length, angle, or rate. The A & B quadrature signals are 90º out of phase, and their phase relationship determines whether up counts (+) or down counts (-) are produced.

One, two or four quadrature transitions may be counted at a maximum combined rate of 250 kHz and be scaled internally to ±999,999. counts. The input circuitry which may be jumpered for either single-ended input signals or for balanced line driver signals. Anti-jitter circuitry eliminates errors produced by vibration of the encoder. In the event of a power failure, the current total may be stored in non-volatile memory and can be used as the starting point for counting when power resumes. Power fail or zero index capabilities are alternate meter setup choices.

A zero index pulse, if available, is interpreted by the meter as indicating a zero reference for an integral number of revolutions of a rotary shaft encoder or the home position of a linear encoder. It is used by the meter for initializing and to correct for any cumulative pulse count errors. Special circuitry corrects for width of the zero index pulse.

Available for Total or Rate

• With the Standard main board, the transmitter totalizes the quadrature counts and then scales the total in software for the serial data output. A zero index Z signal can be added as a third input to the A & B signals.
  
  
• With the Extended main board, the transmitter can can be programmed to output either total or rate or rate. For example, the output can track the speed of a moving slab from the RPM of a roller. The update rate for rate is a programmed gate time + 30 ms + 0-2 pulse periods.

LTM Series serial output transmitters send data via an isolated serial port, which is user configurable for RS232 or RS485 and full or half duplex operation. Three protocols are user selectable: Modbus RTU, Modbus ASCII, or Micron ASCII. Modbus operation is fully compliant with Modbus Over Serial Line Specification V1.0 (2002). The Micron ASCII protocol allows up to 31 Micron devices to be addressed on the same RS485 data line. It is simpler than the Modbus protocol and is recommended when all devices are Microns. It also allows use of Micron Datalogging Software.

Standard features of Micron transmitters include:

• Serial data output, isolated. User selectable RS232 or RS485, half or full duplex, Modbus or Micron ASCII protocol.
• Dual solid state relays for control or alarm, isolated. 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.
• Analog transmitter output, 16-bit, user scalable and isolated. User selectable 4-20 mA, 0-20 mA or 0-10V levels. Generated by an ultra-linear 16-bit (65,536 step) digital-to-analog converter (DAC) for 0.02% output accuracy.
• Universal AC power supply for 85-264 Vac.

Easy Quadrature Transmitter programming is via Micron'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 Micron (P/N CBL04).

Application Examples of Micron
Quadrature Meters & Transmitters

Controlling the repetitive cutting of material to length is an excellent application of a Micron quadrature transmitter or Micron quadrature meter.

The quadrature encoder shares the shaft of a sensing wheel, whose rotation corresponds to lineal displacement of material. The transmitter compares the displacement reading against setpoint information, and then uses its dual relays to first slow down and then cut the material.

Accurate X-Y position or rate can be obtained from two shaft encoders, which convert linear position to quadrature signals as a shaft turns. In addition to serving as a transmitter, each Micron transmitter or meter can use its optional dual relay setpoint capability for closed loop control.

Quadrature can be used to track position and vertical drilling speed of the bit in an oil drilling operation. A shaft encoder is rotated by a cable that moves with the drilling shaft. In this application, the same encoder signal is applied to a Micron quadrature transmitter for position, and to a second quadrature transmitter for rate. Both transmitters can send a 4-20 mA signal to a control room and be alarmed.

In this application, quadrature provides much higher immunity to noise and jitter than a magnetic pickup.