check
check
check
check
check
check
Choose an industrial flow sensor by defining five things in order: the medium (liquid or gas, clean or contaminated, conductive or not, viscous or not), the flow range including minimum and maximum (not just the nominal), the pipe size and available process connection, the pressure and temperature limits at the measuring point, and the output signal the control system accepts. KJT Sensors offers flow measurement products within its measuring-sensor portfolio — confirm the applicable principle and exact model against your medium data before specifying.
The medium decides the principle. Flow measurement technologies are medium-specific: conductivity, viscosity, solids content, and gas versus liquid each rule technologies in or out. Define the medium completely before comparing models.
Size for the range, not the pipe. A flow sensor must measure accurately at minimum flow, not only at nominal. State minimum, normal and maximum flow; the turndown requirement follows from them.
The connection and the environment are specification items. Pipe size, thread or flange standard, pressure rating, temperature, and ingress protection all belong in the request — not just "flow, 4–20 mA".
Incorrect or unstable readings after installation — air bubbles, partially filled pipes, vibration, mounting orientation — are a diagnosis topic covered separately in the flow-sensor troubleshooting guide ({{URL_T18}}); this article covers selection only.
Every flow-technology shortlist starts with the medium:
| Medium property | Why it matters at selection |
|---|---|
| Liquid vs gas | Most principles are designed for one or the other; confirm the stated medium |
| Electrical conductivity | Conductive versus non-conductive liquids rule entire technology families in or out |
| Viscosity | High-viscosity media narrow the viable principles and affect pressure loss |
| Solids, fibers, contamination | Dirty media require obstruction-tolerant designs or upstream conditioning |
| Corrosiveness | Defines wetted-material requirements — state it explicitly |
| Hygiene requirements | Food and pharmaceutical service requires appropriate connection and material standards |
Do not ask "which flow sensor is best" — ask "which principles are compatible with this medium". The second question has an engineering answer; the first does not.
Flow sensors are specified by measuring range, and their stated accuracy applies within that range — typically not at the bottom of it. Provide three numbers:
Minimum flow that must be measured with stated accuracy;
Normal operating flow, which should sit comfortably inside the range;
Maximum flow, including surges and cleaning cycles.
The ratio between maximum and minimum defines the turndown requirement. If a single sensor cannot cover the span with acceptable accuracy at the low end, the engineering options are a different principle with wider turndown, a smaller line section, or accepting reduced low-flow accuracy — decide explicitly rather than discovering the limitation after commissioning.
Distinguish the terms when comparing data sheets: measuring range (the span the device covers), accuracy (error relative to reading or full scale — the basis matters), repeatability (scatter of repeated readings), and response time (how fast the output follows a flow change). They are different parameters; a data sheet that mixes them is not comparable to one that separates them.
Pipe size and connection: the sensor's process connection (thread standard, flange, clamp) must match the line; adapters add leak points and cost.
Straight-run requirements: many flow principles require undisturbed flow profiles — upstream elbows, valves and reducers affect measurement. State the available straight pipe lengths when requesting a recommendation; if installation conditions are constrained, say so.
Orientation: some principles require specific mounting orientations (horizontal versus vertical run, flow direction). Confirm against the model documentation.
Pressure loss: any sensor in the line adds pressure drop; verify the system can tolerate it at maximum flow.
Process pressure: the sensor body and connection rating must cover maximum process pressure with margin.
Process temperature: both medium temperature and ambient temperature at the mounting point matter; electronics and seals have separate limits.
Hazardous areas: explosive atmospheres require appropriately certified configurations — verify model-level certification documents for the exact model; do not assume a standard product is usable.
Analog (4–20 mA, 0–10 V): continuous flow value to a PLC or controller; 4–20 mA is the robust default for long runs.
Pulse/frequency: totalization and rate from pulse counting.
Digital (RS485 and similar): multi-parameter readout and configuration where supported.
Switch outputs: flow/no-flow or threshold alarms.
The integration guide for matching sensor outputs to PLC inputs ({{URL_F10}}) covers the electrical compatibility checks, and the interface-technology comparison ({{URL_T20}}) covers analog-versus-digital selection at the system level.
