Weighing Control Instrument
The weighing control instrument is a microcomputer-based instrument used for dynamic belt scales and batching control. It adopts a human-computer dialogue on the VFD screen and directly displays the weighing flow, cumulative related information in Chinese, making the operation and calibration particularly convenient. The instrument has functions such as automatic zero calibration, automatic interval calibration, automatic fault alarm diagnosis, optical isolation input/output, standard serial ports, and built-in PID control output.
2. Environmental Parameters
Storage Temperature: -40°C to +70°C;
Operating Temperature: -10°C to +50°C;
Relative Humidity: 95%
3. Power Supply
220VAC + 10% ~ - 15%, 50Hz
Fuse: 0.5A
EMI/RFI filter
4. Weighing Sensors
The instrument provides a 10VDC, 200mA excitation power supply and can be connected in parallel with 4 weighing sensors.
Sensitivity: 0.5mV/V - 3.5mV/V
Input signal: 33mV
The weighing sensor is shielded and grounded.
When the cable distance is greater than 60 meters (not exceeding 900 meters), the excitation compensation circuit jumper is used to select local or remote compensation.
5. Main Board Digital Input Ports
The main board of the instrument provides 3 programmable input ports to receive dry contact switch signals.
6. Main Board Digital Output Ports
The main board of the instrument provides 3 programmable output ports with 24VDC open collector output, which can directly drive and control relays.
7. Communication Board
The instrument can be installed with a communication board. It can use standard RS-232 and RS-485 serial interfaces to communicate with the host computer's communication board, collect instrument data and operate the instrument, with two-way communication functions.
8. Main Performance
Four-line display, selected through the menu
5 status indicator lights
Current output of material flow or load
Pulse output of the total weight of materials
Automatic zero adjustment and interval adjustment
Automatic zero tracking
Photocoupled digital input and output
Alarm and fault prompts
Communication functions: RS232, RS485 multi-station communication network
One-way process control mode: PID control output
9. Main Functions
All function software is 固化 (firmware) in the memory chips. When the user installs the optional expansion board or the operator selects through the keyboard, the controller will automatically activate the corresponding functions.
(1) Measurement Functions
a. Instantaneous Flow Calculation: The signal of unit weight output by the weighing sensor is multiplied by the signal of unit belt speed output by the speed sensor, and the result is the instantaneous flow.
b. Weight Accumulation: The accumulated amount is the product of the weight per unit length and the running length, and then converted into engineering units.
c. Automatic Zero Adjustment and Automatic Interval Adjustment: Defining the number of belt loops and the length of the belt is the basis for automatic zero adjustment and automatic interval adjustment. To accurately calculate the belt length, the controller calculates the number of pulses sent by the speed sensor. When the accumulated number of pulses reaches the required value, the controller ends the calibration test, compares the theoretical value with the actual value, and calculates the calibration constant.
d. Automatic Zero Tracking: When the belt is running and the flow is lower than the preset value, the controller performs automatic zero adjustment according to the following steps:
Wait for half of the test cycle time (display "Z")
Complete one zero adjustment test
Complete the automatic zero adjustment for one test cycle
As long as the flow value is lower than the preset value of the automatic zero tracking, the instrument will continuously repeat the above steps.
e. One-way Input, Two-way Current Output Signals: Optional input/output expansion boards can be used to obtain one-way voltage/current input and two-way current output signals.
(2) Monitoring Functions
Status prompts
Process alarms
Setting errors
Equipment failures
High flow, low flow, high load, low load alarms
(3) Automatic Control of Feeding Function
The weighing controller provides an independent control current loop, which is usually used to control the feeding amount. The control method is as follows:
PID = Proportion + Integration + Differentiation
The controllable process variable is the feeding amount. The flow setting can be input through the keyboard or set by an external analog signal. The control output is a 4 - 20mA current loop.
