The JMSC900 series of wall panel mounting control units provide comprehensive control functionality for any 4-20 mA or HART compatible transmitter. A back-lit display gives clear visual indication of the measured value and status of all inputs and outputs. Mounted in a non-hazardous area, the main powered JMSC900 provides a protected 24V dc power supply to the transmitter, which may be installed in a hazardous area. The input signal from the transmitter may be offset, damped, scaled, and linearized as required. A range of pre-programmed linearization algorithms are user selectable. The 4-20 mA output signal may also be scaled to re-transmit all or just part of the input signal or calculated value. Five relays are provided and are fully field programmable to perform a wide variety of control, fault indication or alarm duties.
Ultrasonic transmitters send a pulse of ultrasound down to the liquid surface and detect the reflected echo. An internal microprocessor, which is pre-programmed with the speed of sound, can then translate the time taken for the pulse to be returned into the distance between the transmitter face and the liquid surface. An integral temperature sensor in the transmitter compensates for temperature change effects on the speed of sound in the ullage space.
Having established this basic distance, the transmitter calculates the depth of the liquid and sends this information back to the control unit as a 4-20mA signal proportional to the level. Alternatively, a ceramic cell hydrostatic pressure transmitter can be used to sense the liquid level and provide the 4-20mA signal to the control unit.
The control unit uses this information to drive control relays which can be freely assigned by the operator. Alternatively, tank contents or volumetric flow in an open channel flow application can be calculated.
There are 5 built-in relays and a 4-20mA current output. A clear 4 line display on the unit shows the measured variable or may be programmed to show other operational information. A bar graph representation of the current output and relay status are also displayed.
Programming is simple and efficient using the integral membrane keypad on the face of the control unit. The menu structure is easy to navigate with the built in programming “Wizard” configuration is fast and error free.