Rangeable describes a type of measurement instrument that has an output signal which can be adjusted by the operator to a different scaling.
A rangeable instrument can be rescaled by adjusting the zero and span setting to a measurement between zero and the 100% full scale range of the instrument.
The different methods used to re-range a measurement instrument output include externally accessible variable potentiometers, push button controls or digital communications.
Some rangeable instruments have a limit on how much the scale can be reduced, which is typically expressed as a ratio of the maximum full scale. For example a 10 bar range pressure transmitter which can be reduced by up to 80%, would be described as having a 5 to 1 turndown ratio.
Often the accuracy performance will be compromised when a range is re-scaled to a reduced span, particularly with analogue based devices.
Some digital rangeable devices will offer a fixed percent of full scale accuracy to a certain level of turndown, beyond which the percent full scale accuracy will typically increase pro-rata.
- Rangeable Pressure Transmitters - Rangeable pressure transmitter which can be down-ranged by the operator to scale the 4 to 20mA output signal to a different pressure range.
- Rangeable DP Sensors - Rangeable differential pressure sensors with output signals that can be adjusted by the user to elevate or suppress the zero position and turn down the full range span.
- DS201P High Range Flush Pressure Gauge, Switch and Sensor
- DPS300 User Switchable Pressure Range, Volts or Current Output Low DP Sensor
- 33X High Accuracy Digital Output Pressure Sensor
- DS200P Sanitary Low Range Pressure Gauge, Switch and Sensor
- DPT200 Pressurised Tank Level Differential Pressure Transmitter
- DPT200 High One Side Overload Differential Pressure Sensor
- PD39X High Differential Pressure Transmitter
- PD33X High Accuracy Differential Pressure Transmitter
- PD33X Digital Differential Pressure Sensor
- XMD Process Plant DP Cell Differential Pressure Transmitter
- PD39X Twin Absolute Digital DP Sensor
- LEO3 Current or Digital Output Pressure Gauge
- 35X Flush Diaphragm Digital Output Pressure Sensor
- DMP331i High Accuracy Pressure Transmitter
- DMP333i Rangeable High Pressure Precision Transducer
- XMPi Process Plant Gauge and Absolute Pressure Transmitter
- DS200 Combined Pressure Switch, Gauge and Sensor
- DS210 Combined Low Pressure Switch, Indicator and Sensor
- 41X High Precision Low Range Pressure Transmitter
- x|act i Rangeable Flush Pressure Transmitter with LCD Readout
- 36XW Digital Submersible Hydrostatic Level Sensor
- 140 inch range rangeable 4-20mA output wastewater level sensor and display for external fitting - A digital display combine with a rangeable externally mounted liquid level sensor for measuring the height of wastewater over a range of 0 to 140in from the 1/4 NPT male process connection, and sending the corresponding 4-20mA signal through the M12 connector electrical connection.
- Water reservoir rangeable submersible depth transmitter - Rangeable submersible depth transmitter with a digital interface for re-ranging to any depth down to 10 m max.
- Adjustable range pressure sensor for scaling -1 to +1 bar g - Rangeable high accuracy pressure transducer with a 0-10V output signal, a compound pressure range of -1 to +1 bar (-15 to +15 psi) gauge.
- 100 mbar abs vacuum transmitter with a 5 bar overpressure - 4-20 mA signal vacuum transmitter with a 0 to 100 mbara range which can withstand a 5 bar absolute overpressure.
- Zero and span adjustable 10 bar ATEX pressure transmitter - ATEX approved intrinsically safe pressure transmitter with zero & span adjustability over a maximum of 10 bar gauge
- HART flameproof (Ex d) re-scalable level transmitter for hydrostatic head up to 2 metres - HART compatible, ATEX flameproof approved, rangeable level transmitter to measure hydrostatic head of water/glycol or mineral oil fluid within a reservoir about 2 metres in height.
- 7mH2O hydrostatic level sensor with 4-20mA plus HART - HART communications enabled 4-20mA output hydrostatic level sensor with a range of 0 to 7 metres of water column.
- Water tank level gauge transmitter with adjustable range - We are looking for level measurement gauge transmitters for water tanks used for domestic water and fire water in a hotel.
Turn down accuracy
For a rangeable transmitter of lets say 100 bar g full scale, and a 100:1 turn down with an accuracy of 0.1%FS, the error would be +/-100 mbar over the range of 0 to 100 bar g. What would be the accuracy if it was re-ranged to 60 bar. Would it be +/-100mbar or +/-60mbar?
It will depend on the make and type, since some will improve the accuracy at lower ranges by using a % of reading method. The worse case error should be within 100 mbar at any point or range. You should be able to find some statement on the product data sheet explaining how the accuracy is affected by turndown.