Power management - WXT530

WXT530 Series User Guide

Document code
M211840EN
Revision
F
Language
English (United States)
Product
WXT530
Document type
User guide

The power consumption varies significantly, depending on the selected operating mode or protocol, the data interface type, the sensor configuration, and the measurement and reporting intervals.

Lowest consumption is achieved with the native SDI-12 mode, typically about 1 mW in standby (0.1 mA at 12 V), while with ASCII RS-232 or continuous SDI-12 modes it is about 3 mW in standby. Any activated sensor measurement adds its own extra consumption to the standby power.

Some hints for economic power management are given below. The consumption values are all defined for 12 V supply. For 6 V supply, multiply the values by 1.9. For 24 V supply, multiply the values by 0.65.

Table 1. Standby power consumption
Mode Standby Wind
4 Hz sampling rate 1 Hz sampling rate
Continuous measurement 10 s average every 2 min Continuous measurement 10 s average every 2 min

RS-232

RS-485

RS-422

SDI-12 continuous

1.5 mA +4.5 mA + 0.6 mA +1.3 mA +0.2 mA
SDI-12 native 0.1 mA N/A +1 mA N/A +0.7 mA
Analog output (mA) N/A 16 … 90 mA 16 ... 90 mA 16 ... 90 mA 16 ... 90 mA
Mode Standby PT1000 Level Tipping bucket Solar radiation Precipitation
Continuous rain

RS-232

RS-485

RS-422

SDI-21 continuous

1.5 mA +0.1 mA +0.4 mA +0.1 mA +0.4 mA +0.4 mA
SDI-12 native 0.1 mA +0.1 mA (interval 5 s) +0.4 mA (interval 5 s) +0.1 mA (interval 1 s) +0.4 mA (interval 5 s) +0.4 mA (interval 5 s)
Analog output (mA) N/A N/A N/A N/A N/A N/A
SDI-12 native mode power save is based on measurements only when requested. Due to SDI-12 polling mode operation, only periodic wind measurement results are comparable with other communication modes. Continuous measurement is not relevant for SDI-12 mode. Every measurement request increases power consumption for the first time measurement. The total SDI-12 power consumption can be changed by changing measurement request intervals.
Figure 1. PTU power consumption in RS-232, RS-485, RS-422, and SDI-12 continuous modes
Figure 2. PTU power consumption in SDI-12 native mode
Table 2. Economic power management
Measurement Consumption
Wind measurement The most consuming operation in the system, with extra variations depending on how the wind is reported. If you need long time averages and measure wind constantly, there are no large differences between requesting periods or modes. Fully continuous wind measurement with a 4 Hz sampling rate adds about 4.5 mA to the standby current, depending on the wind and some other climatic conditions. A 10-second average requested every 2 minutes consumes 8 times less. 1 Hz sampling rate decreases it to about one fourth.
Continuous precipitation Adds approximately 0.4 mA to the standby consumption. A single, isolated raindrop increases current consumption for about 10 seconds (continued, if more raindrops are detected within the 10-second period).
ASCII RS-232 Standby consumption Typically 1.5 mA. The jumper wires across TX+/RX+ and TX-/RX- (only necessary in 2-wire RS-485) increase consumption slightly.
ASCII RS-232 Polling mode and Automatic mode Equal consumption. The automatic mode is a little more economic, since interpreting the poll takes more processing time than starting the Automatic message. However, note that when selecting the precipitation auto-send mode, the sub-modes M=R and M=C can cause extra consumption in rainy conditions due to triggers for sending messages about rain incidents.
ASCII RS-232 Data transmission Adds 1 ... 2 mA to the standby consumption during the message sending time. Note that the host device's input (data logger or PC) can constantly draw some current from the TX line.
RS-485 and RS-422 Data interfaces Consume about the same amount of power as RS-232. With long data cables the data consumption during data transmission can be much higher, especially when termination resistors are used. On the other hand, the RS-485 driver is in high impedance state when not transmitter. In idle state, no current can be drawn by the host input.
NMEA modes They consume about the same as ASCII modes.
SDI-12 Native mode M=S, C=1 has the lowest stand by consumption, about 0.1 mA. Note that it can also be used with RS-232 terminals. See the SDI-12 connection diagram in Data communication interfaces. In this case, the commands must be in SDI-12 format, but no special line break signals are required. The SDI-12 mode is for polling only.
SDI-12 Continuous mode M=R consumes about the same as the ASCII RS-232 mode.

If the optional sensor heating is enabled, SDI-12 Native mode consumes the same as ASCII RS-232 mode.

When heating is on (or the temperature is such that it should be on), some 0.08 mA additional current is drawn from the operational power supply.

While in Service mode and/or while supplied through the service port the transmitter consumes 0.3 ... 0.6 mA more than in normal mode, when supplied through the main port (M12 connector or screw terminals). When supplied through the service port the minimum voltage level for reliable operation is 6 V. This can also be seen in the supply voltage reading of the Supervisor message - the Vs value is 1 V lower than the actual input voltage.