The SPX Wellhead maintains its own RTC (Real Time Clock). The RTC is synchronized to the AquaVent datalogger on power-up, else defaults to a start-up time of 0:00:00.0, Jan. 01, 1970. When the time is requested, the RTC will be re-synchronized to the AquaVent logger, if it has not been synchronized recently.
If an AquaVent logger is changed, it is recommended to sync the Wellhead clock to the new logger. This can be done by disconnecting the RS232/RS485 Connector Cable from the Wellhead, then re-connecting after 30 seconds.
Since the Wellhead clock is used to provide time-stamps with real-time data, and may be less accurate than the AquaVent logger clock, it is recommended to periodically force a re-sync for best accuracy. This can be done by programming the MODBUS master to read the "current time" register set, about once per day.
Upon initial power-up, or after receiving any properly addressed MODBUS command over the RS-232 interface, the MODBUS RS-232 interface is powered up, waiting to receive the first command. With the MODBUS RS-232 interface in standby, the Wellhead draws about 3mA while connected to the customer equipment, depending on how much that equipment loads the data line.
If a properly addressed command is received through RS-485, then the RS-232 interface enters power saving mode, in which it no longer transmits any voltage (not a valid line condition) onto the data line. At this time the Wellhead idles with a supply draw of about 30uA, while still listening to the RS-232 interface.