Process measurement instrument adapted for wireless communication

• US 8,447,367 B2
• Filed: 05/07/2007
• Issued: 05/21/2013
• Est. Priority Date: 05/07/2007
• Status: Active Grant

• Current Assignee: Rosemount Tank Radar AB (Emerson Electric Company)
• Original Assignee: Rosemount Tank Radar AB (Emerson Electric Company)
• Inventors: Wenger, Fabian
• Primary Examiner(s): Figueroa, Marisol
• Application Number:
  US11/800,605
• Publication Number:
  US 20080278145A1
• Time in Patent Office: 2,206 Days
• Field of Search: 455/574, 732/90.R, 732/91, 340/618
• US Class Current: 455/574
• CPC Class Codes: G01F 23/284 Electromagnetic waves
• CPC Class Codes: G08C 17/04 using magnetically coupled devices
• CPC Class Codes: H04Q 2209/43 using wireless personal area networks [WPAN], e.g. 802.15, 802.15.1, 802.15.4, Bluetooth or ZigBee
• CPC Class Codes: H04Q 2209/883 where the sensing device enters an active or inactive mode
• CPC Class Codes: H04Q 9/00 Arrangements in telecontrol or telemetry systems for selectively calling a substation from a main station, in which substation desired apparatus is selected for applying a control signal thereto or for obtaining measured values therefrom

Abstract

A process measurement instrument adapted for wireless communication, comprising a measurement unit (7) arranged to determine a measurement value of a process variable, a memory (21) arranged to store a current measurement value of the process variable, a wireless communication unit (8), arranged to access the current measurement value and communicate the current measurement value over a wireless communication channel according to a protocol with intermittently active communication, and arbitration logic (22), in communication with the measurement unit and the wireless communication unit, and arranged to ensure that active periods of the measurement unit occur when the wireless communication is inactive.

The measurement unit and communication unit are thus able to share information via the common memory, e.g. by sequential read/write access. This avoids the need for simultaneous activity. The invention can be especially advantageous when the instrument is powered by an internal power store, such as a battery, and extend the lifetime of such a power store.

Claims

1. A process measurement instrument configured for wireless communication, comprising:

a measurement unit configured to determine a measurement value of a filling level of a product in a tank,

said measurement unit having an operation comprising active time periods and inactive time periods, said active time periods having higher power consumption than said inactive time periods,

a memory configured to store a current measurement value of said filling level,

a wireless communication unit, configured to access said current measurement value and communicate said current measurement value over a wireless communication channel according to a communication protocol,

wherein said communication protocol is a time division multiple access (TDMA) protocol, and relies on specific timing controlled externally of said process measurement instrument, wherein said wireless communication unit has active periods during TDMA communication slots allocated by said communication protocol, and inactive periods between said active periods, and

arbitration logic, in communication with said measurement unit and said wireless communication unit,

wherein said arbitration logic controls the active periods of the measurement unit to occur between active periods of said wireless communication unit for avoiding power consumption spikes and interference in said process measurement instrument.

2. A process measurement instrument according to claim 1, wherein a measurement cycle of said measurement unit is divided over several active periods.

3. A process measurement instrument according to claim 1, wherein said instrument further comprises an internal power store.

4. A process measurement instrument according to claim 1, wherein said instrument further comprises a wireless interface for power supply.

5. A process measurement instrument according to claim 1, wherein said measurement unit comprises a transceiver for transmission of electromagnetic waves during said active periods.

6. A process measurement instrument according to claim 1, wherein said arbitration logic is configured to prolong an inactive period of said measurement unit, so as to delay a subsequent active period until the wireless communication unit is inactive.

7. A process measurement instrument according to claim 1, configured to determine the level of a product in a tank, comprising

a transceiver for transmitting and receiving electromagnetic signals,

a propagation device configured to allow a transmitted signal to propagate towards said surface, and to return a reflected signal to the transceiver, and processing circuitry for determining said measurement value based on a relationship between said transmitted signal and said received signal.

8. A method for communicating a measurement value of a filling level of a tank from a measurement unit configured to transmit electromagnetic signals, receive a reflected signal from said tank, and determine said measurement value based on a relationship between a transmitted signal and a received signal, said measurement unit having an operation comprising active time periods and inactive time periods said active time periods having higher power consumption than said inactive time periods, said method comprising the steps of:

storing a current measurement value of said filling level,

accessing a stored current measurement value,

communicating said current measurement value by means of a communication unit over a wireless communication channel according to a communication protocol with intermittently active communication,

wherein said communication protocol is a time division multiple access (TDMA) protocol and relies on specific timing controlled externally of said process measurement instrument, wherein said wireless communication unit has active periods during TDMA communication slots allocated by said communication protocol, and inactive periods between said active periods, and

controlling the active periods of the measurement unit to occur between said active periods of said wireless communication unit for avoiding power consumption spikes and interference in said process measurement instrument.

9. The method according to claim 8, wherein a measurement cycle of said measurement unit is divided over several active periods.

10. The method according to claim 8, wherein said step of controlling comprises prolonging an inactive period of said measurement unit, so as to delay a subsequent active period until the wireless communication unit is inactive.