The STs series of submersible water quality transmitters have an integrated preamp and an isolated 'true 2-wire', 4-20 ma transmitter. Two independent channels simultaneously transmit a dissolved oxygen (DO) and temperature signal -- two wires for DO and two wires for temperature. The compact design afforded by the patented pHiConn (TM) keyless connection system -- and the 316SS (titanium optional) and Delrin construction -- make the rugged sensor/transmitter ideal for applications such as process control, data acquisition, wastewater treatment, and, groundwater monitoring, The units can be submersed to 200 feet (approximately 100 psi). Individual units can be combined to make redundant or multiparameter modules using the pHionics' patented pHiKLIP (TM) array system. The pHiKLIP (TM) system also allows for the units to be used in in-line (insertion) applications without fear of blow-out. As with all pHionics' designs, the sensor/transmitters are designed with 'ease of service' as a primary goal.
The 'true 2-wire', 4-20 ma STs series sensor/transmitters send a current proportional to the parameter being measured on the same two wires that provide the power (7 to 40 volts dc). Current transmission allows for long runs of inexpensive cable or wire (up to three miles) that is virtually noise-free without any signal loss that is common to voltage (IR drop) or digital (capacitance affecting 'rise/fall' timing). The seven volt operation allows the units to be powered by 12 volt battery systems with 5 volts of compliance, making them compatible with RTU's and solar powered applications. The units are intended for calibration via software supplied with the datalogger, PLC, or through the DCS.
The dissolved oxygen signal on Channel 1 is automatically temperature compensated -- correcting for membrane and solution temperature changes. This is not to be confused with the temperature channel of the transmitter, which provides an independent, isolated, 4-20 ma output proportional to the 0 to 50 Celsius range on Channel 2. The auto-polarity correction feature directs the applied supply voltage to allow for proper operation regardless of wire hookup. The Red and Black wires are for Channel 1 -- dissolved oxygen, and the White and Green wires are for Channel 2 -- temperature.
The large surface area of the sealed, galvanic measuring cartridge allows for accurate operation of the transmitter within minutes of installation. This is unlike the delays common to typical sensors that can sometimes take 24 hours to stabilize after installation or membrane/solution replacement. The sealed cartridge concept also reduces the man-power that is required with other sensors that often need to be refilled and have the membrane replaced every six months -- and the inherent problems associated with the process. The 30 month typical cartridge life results in a nominal cost of ownership of $14/per month, and can be replaced within 15 seconds -- further lowering costs, and simplifying use.