Yokogawa 414 Batch Controller Manuale Utente Scaricare il pdf (Pagina 41)

6. INPUT CIRCUITS

6.1 THE SIGNAL INPUT

The basic circuit of the input is shown below. Both the current and voltage

signals are fed to a data selector but only one signal is processed, depending

upon whether a current (4-20mA or 0-20mA) or a voltage (1-5 V or 0-10 V)

input configuration is selected. The signal is fed to a voltage to frequency

convertor and transmitted to the microprocessor via an opto-coupler.

The microprocessor uses a crystal reference to provide an accurate measurement

of the incoming frequency. Once every 10 minutes a stable and accurate internal

reference is sampled and used to compensate the input. This technique ensures a

highly accurate measurement and makes periodic calibration unnecessary.

Input Circuits 39

Voltage to

Frequency

Microprocessor

Regulator

DC to DC

Convertor

Reference

10K

250

Ohm

Isolation

Voltage

Current

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Yokogawa 414 Batch Controller Manuale Utente Pagina 41