Emerson MICRO MOTION 2700 Manual de Instalação descarregar pdf (Página 72)

62 Transmitter Configuration and Use: Series 1000 and 2000 Transmitters

Required Transmitter Configuration continued

The default pulse width is 277 milliseconds, which yields a crossover frequency of 1.8 Hz. In other

words, above 1.8 Hz, the transmitter’s frequency output will use a 50% duty cycle. At frequencies of

1.8 Hz or lower, the pulse width will be 277 ms. In both cases, the process variable is represented by

the number of pulses per unit of time.

The transmitter’s maximum crossover frequency is 922 Hz. This corresponds to a pulse width of

0.543 ms.

You can change the setting for maximum pulse width so that the transmitter will output a pulse width

appropriate to your receiving device:

• High-frequency counters such as frequency-to-voltage converters, frequency-to-current

converters, and Micro Motion peripherals usually require approximately a 50% duty cycle.

• Electromechanical counters and PLCs that have low-scan cycle rates generally use an input

with a fixed nonzero state duration and a varying zero state duration. Most low-frequency

counters have a specified requirement for the maximum pulse width.

Note: For typical applications, the default pulse width is used.

Note: If you are using the Freq = Flow output scale method, and you set maximum pulse width to a

value below 277 ms, Micro Motion recommends setting the frequency factor to a value below 200 Hz.

See Section 6.6.2.

6.6.4 Configuring the frequency output polarity

The frequency output polarity controls how the output indicates the active (ON)

state. See Table 6-12. The default value, Active high, is appropriate for most

applications. Active low may be required by applications that use low-frequency

signals.

Example

The frequency output is wired to a PLC with a specified pulse width

requirement of 50 ms. The crossover frequency is 10 Hz.

Solution:

• Set Max Pulse Width to 50 ms.

• For frequencies less than 10 Hz, the frequency output will have a

50 msec ON state, and the OFF state will be adjusted as required.

For frequencies higher than 10 Hz, the frequency output will be a

square wave with a 50% duty cycle.

Table 6-12 Polarity settings and frequency output levels

Polarity Reference voltage (OFF) Pulse voltage (ON)

Active high 0 As determined by power supply,

pull-up resistor, and load (see the

installation manual for your

transmitter)

Active low As determined by power supply,

pull-up resistor, and load (see the

installation manual for your

transmitter)

• Model 1500 AN

• Model 1700 AN

• Model 1700 IS

• Model 2500 CIO

• Model 2700 AN

• Model 2700 IS

• Model 2700 CIO

1 2 ... 67 68 69 70 71 72 73 74 75 76 77 ... 263 264

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