Theory Of Operation; Functional Blocks; User Interface; Preamplifier - Hoffer Flow Controls HIT-2A User Manual

3. THEORY OF OPERATION

The HIT-2A consists of six functional blocks. These functional blocks
are the User Interface, Preamplifier, Microcontroller, Loop Driver,
Pulse and Alarm Output, and Communications Interface.
Preamp
Flowmeter Input
Communications
RS232
Interface
IRDA
3-1

Functional Blocks

3-1-1

User Interface

The User Interface consists of a custom LCD display with 4 push
buttons; OK, P, > (right arrow), and ^ (up arrow) and an optional
external reset. Using the buttons and the displayed information,
the user can enter setup parameters (rate units, pulses per unit of
flow, etc.) as well as setup information for the pulse output and 4-
20mA output. The optional external reset maybe used to reset the
accumulated total to zero and clear the displayed accumulated
total.
3-1-2

Preamplifier

The Preamplifier accepts the input from the flowmeter.
Preamplifier applies amplification, low-pass filtering, and wave-
shaping to the input signal. The wave shaping function converts
the signal into a square-wave before sending it to the

Microcontroller.

3-1-3 Microcontroller
The Microcontroller accepts the square-wave output of the
preamplifier and performs all of the calculations that are required
to control the Loop Driver. After measuring the frequency of the
Theory of Operation
Microcontroller
User
Interface
Loop Driver 4-20 mA
Opto-isolated
Pulse Output
Outputs
Alarm Output
HP-306
7
The