『Flow Meter Electrical Symbol Identification: Reading Wiring Diagrams and Schematic Prints』Related information(v cone flow meter|rotary gas meter|gallon meter|gear meter|metal tube rotameter|glass tube rotameter|nutating disk meter|transit time ultrasonic flow meter|wedge flow meter|pd meters|hydraulic flow meter|ultrasonic water flow meter|water flow meter|air flow meter|magnetic water flow meter|oxygen flow meter|gas flow meter|argon flow meter|air velocity meter|gasoline flow meter|fuel flow meter|ultrasonic water meter|digital water meter|nitrogen flow meter|solid flow meter|Oxygen tank flow meter|digital water flow meter|diesel fuel flow meter|steam flow meter|02 flow meter|compressed air flow meter|oil flow meter|liquid flow meter)
Flow Meter Electrical Symbol Identification: Reading Wiring Diagrams and Schematic Prints
Quick Answer: Most flow meter wiring diagrams show the transmitter as a circle or rectangle with a tag number. The loop symbol normally represents the 4-20 mA HART output, and the terminal block shows where power, pulse, and RS485 Modbus wires land. Match the wire tag on the schematic print to the same code on the meter terminal card before you ring out any cable.
Engineers and panel builders often ask how to match a wiring diagram to the physical flow meter. The fastest way is to read the instrument tag, the terminal numbers, and the loop sheet side by side. A typical magnetic flow meter from Silver Automation Instruments has separate terminals for 24 V DC power, 4-20 mA HART output, pulse output, and RS485 Modbus. Each terminal code on the schematic print repeats on the nameplate or on a label inside the housing.
Common Electrical Symbols on Flow Meter Schematic Prints
You will see a few symbols over and over. A circle with a tag number like FE-101 or FIT-101 indicates a flow element or flow transmitter. A bubble with a line to a PLC input card is the loop. A small rectangular block with numbered terminals shows the junction box or the meter terminal strip. A twisted pair symbol with a ground shield means the cable shield must land only at one end, usually inside the panel. A ground symbol with PE marks the protective earth terminal. A box with an X inside means an intrinsic safety barrier or isolator depending on the plant standard.
Some drawings show a square box with two connection points for a loop powered flow meter. This is common for pressure transmitters and some vortex flow meters. A four wire flow meter symbol often has extra power terminals marked L and N for 220 V AC or plus and minus for 24 V DC. Do not assume every flow meter uses the same power. We have seen customers in Vietnam connect a 220 V AC meter to a 24 V DC loop and damage the transmitter board.
Reading Magnetic Flow Meter Wiring Diagrams
A magnetic flow meter schematic print usually separates power, analog output, pulse output, and digital communication. On Silver Automation Instruments electromagnetic flow meters, terminal codes often follow this pattern: L and N for AC power, PE for ground, IOUT and ICOM for 4-20 mA HART, POUT and PCOM for pulse, and A and B for RS485 Modbus. Some models include an empty terminal for a remote display or a PT100 temperature input. The wiring diagram inside the terminal cover matches the loop drawing. If the cable schedule says two pairs screened 0.5 mm2, do not substitute one unshielded cable.
Grounding matters more on a magnetic flow meter than on most other flow technologies. The schematic print will show a PE terminal and sometimes a ground ring symbol. In a wastewater plant in the Philippines, a missing ground ring caused unstable flow readings at low velocity. The wiring diagram looked correct but the electrical path to earth was not complete. For DN15 to DN80 meters with PTFE liners, grounding rings are standard on many Silver Automation Instruments designs.
Loop Drawings and 4-20 mA HART Signals
A loop drawing for a flow transmitter is simple in most cases. The 24 V DC power supply feeds one side of the loop. The positive terminal of the flow meter goes to the positive of the power supply. The negative terminal of the meter goes to the positive input of the PLC or controller. The negative of the PLC input returns to the negative of the power supply. A HART communicator can connect across the resistor in the loop without breaking the circuit.
On a four wire flow meter, the analog output is normally active. The meter supplies the loop current and the PLC reads the signal. This is different from a two wire pressure transmitter where the same two wires carry power and signal. Before you wire a Silver Automation Instruments Coriolis flow meter or magnetic flow meter, check whether the output is active or passive. Most of our meters ship with an active 4-20 mA HART output as default. If your PLC only accepts passive inputs, tell us before dispatch and we will con
Pulse and Digital Output Symbols
Pulse output symbols on flow meter schematic prints usually appear as a square wave icon or a terminal labeled POUT and PCOM. Pulse outputs drive a batch controller or a totalizer. The frequency often scales with flow rate, for example 0 to 1000 Hz across the flow range. Silver Automation Instruments oval gear flow meters for diesel and chemicals use a magnetic pickup pulse output. The signal wires connect to a counter or a PLC high speed input. The drawing shows a shielded twisted pair from the meter to the panel. Keep the pulse cable away from VFD motor cables because noise can create extra pulses and wrong totals.
Power Supply and Protection on Schematic Prints
The electrical symbol for a flow meter on a P and ID does not always show the power supply. The wiring diagram or loop sheet does. For a Silver Automation Instruments thermal mass flow meter, the power terminals accept 24 V DC or 220 V AC depending on the order code. For ATEX Zone 1 or Zone 2 installations, the schematic print will show an intrinsic safety barrier or an explosion proof connection. Never wire an ATEX flow meter without the barrier shown on the drawing. A gas terminal in the Middle East once ordered a meter for Zone 2 but used a standard cable gland. The local inspector rejected the installation. We now send a checklist with every hazardous area order.
A Practical Reading Sequence for Field Technicians
Here is the thing. Most engineers skip the drawing notes and go straight to the terminals. That causes wiring errors. Start with the instrument index and find the tag number. Then open the loop sheet for that tag. Read the cable schedule. Check the terminal numbers on the flow meter wiring diagram. Match the wire tags to the physical cable cores. Verify the power supply voltage before you close the breaker. In practice, a five minute check stops a two hour fault search.
For Silver Automation Instruments meters, we include a wiring card inside every shipment. The card uses the same terminal codes as the schematic print. If your plant drawing uses a different tag format, send us the drawing and we will mark it up. Send us your power supply, output type, pipe size in DN, flow range in kg/h or m3/h, pressure in bar, fluid temperature in °C, and hazardous area classification. Tel: +86-25-68650347. WhatsApp: +86-25-52155837. WeChat: +86 15365082610.
FAQ: Flow Meter Electrical Symbol Identification
1. What is the symbol for a flow transmitter on a wiring diagram?
The flow transmitter is usually a circle with a tag number, or a rectangle with terminal numbers. The circle location on the loop drawing shows that the device is part of a 4-20 mA loop.
2. How do I read terminal labels on a magnetic flow meter?
Open the terminal cover and compare the printed label with the loop drawing. Common labels are L, N, PE, IOUT, ICOM, POUT, PCOM, A, and B. One terminal block is for power, another is for signal.
3. What does the loop symbol with a 4-20 mA arrow mean?
It means the flow meter sends an analog current signal to the control system. A 4 mA reading normally equals zero flow and a 20 mA reading equals the full scale flow set in the meter.
4. Why do some flow meters need separate power and signal cables?
A four wire flow meter uses one cable for power and another for output. This prevents AC supply noise from coupling into the pulse signal or the 4-20 mA loop.
5. Can Silver Automation Instruments provide wiring diagrams before purchase?
Yes. We send product drawings, terminal diagrams, and installation notes before shipment. If you have a project drawing, send it to us and we will mark up the terminal codes to match your system.
Need a specific wiring diagram for a magnetic flow meter, Coriolis flow meter, ultrasonic flow meter, vortex flow meter, or oval gear flow meter? Send us your supply voltage, cable entry size, pipe size in DN, and output signal list. We reply with a matching drawing and price for the project.
Hot Blog
Related AD
