E+H Servo Level Transmitter Commissioning

The NMS81 intelligent servo level transmitter operates based on the displacement measurement principle and is designed for high-precision liquid level measurement systems.

Detection Procedure: A stepper motor positions the float within the liquid medium. The float is suspended on a measuring cable wound around a drum. The NMS81 calculates the drum’s rotation count to determine the measuring cable’s displacement, thereby deriving the liquid level change.

When the float descends and contacts the liquid, buoyancy reduces its weight. A magnetic sensor measures this weight change, inducing torque variation in the coupling magnet. Six Hall sensors measure this torque variation. The float weight signal is sent to the motor control circuit, driving the motor to adjust the float position as the liquid level rises or falls. A magnetic rotary encoder continuously calculates drum revolutions to determine the liquid level. Beyond liquid level measurement, the NMS81 can also measure up to three liquid phase interfaces, tank bottoms, as well as single-point and gradient density.

Instrument Commissioning

1. Set the real-time clock. Menu path: Settings → Advanced Settings → Date/Time → Set Date. Configure the real-time clock to the current date and time: Year, Month, Day, Hour, Minutes.

2. Set the device ID. Modify or configure the device ID via the menu path: Settings → Device ID.

3. Set the density. Density values should be configured based on design data or as provided by process personnel. For level measurement, only the upper medium density needs to be set; intermediate and lower medium densities are not involved in level calculations. Menu path: Settings → Upper Medium Density; Settings → Intermediate Medium Density; Settings → Lower Medium Density.

4. Set instrument range: Menu path: Settings → Advanced Settings → Input/Output → Analog IP B1-3 → HART Output → Settings → 0% Value, enter the lower limit value (typically 0 mm);

Settings → Advanced Settings → Input/Output → Analog IP B1-3 → HART Output → Settings → 100% Value, enter the upper limit value based on the design range upper limit.

5. Configure communication information: If the instrument has communication signals like RS485, input them here. Menu path: Settings → Advanced Settings → Communication → Modbus X1-4 → Settings. Typically, only the 485 address information needs to be set. If multiple instruments are on the bus, the terminal resistor setting for the farthest instrument must be set to Open in this item.

6. Execute the bottom-level command to measure tank bottom data: Menu path: Operation → Tank Command → Tank Command → Bottom Level. Select the Bottom Level command in Tank Command. The float descends to automatically locate the bottom. Upon reaching the bottom, the command automatically changes from Bottom Level to Level. Wait for the distance value to stabilize, then record this value.

7. Return to the Settings menu. Locate Empty Tank Height, Tank Reference Height, and Upper Stop Position sequentially. Input the recorded bottom-level value. Then set the Lower Stop Position to 300 mm.

8. After inputting values, return to Operation → Tank Gauge Commands → Tank Gauge Commands. Select the Up command. The float will ascend and eventually stop at the reference height position.

9. If no material is currently entering the tank, select the Stop command to halt the instrument motor (Note: Do not execute the level command if the tank is not receiving material). Instrument setup is now complete.

10. Instrument Commissioning: Once material enters the tank to a certain height (exceeding the lower stop position), navigate to Operation → Tank Gauge Command → Tank Gauge Command and select the level command. The instrument will automatically locate the actual liquid level and commence measurement.

11. Instrument Precautions:

• The instrument housing must be grounded locally.

• The instrument cannot withstand pressure surges, as this may cause the steel cable to break easily. Open the bottom valve slowly and fully only after pressure stabilizes;

• Before closing the bottom valve, always confirm through the glass window that the float has risen to the reference height; failure to do so may cause the steel cable to be crushed and broken;

Residual pressure remains between the root valve and instrument chamber when opening the glass sight window or magnetic drum rear cover. Avoid potential injury from pressure exposure.