General Characteristics

Vl 92 has been designed to fulfil any requirement for the visualization of signals coming from measuring instruments, especially in the water treatment field. The whole line made available covers any possible application, from small-size household plants to medium and large-size industrial ones. The constructional criteria have been such as to ensure maximum reliability in a number of operating conditions. Besides its displaying function, Vl 92 can act as a Proportional Controller (IF) able to control a metering pump with automatic setting of flowrate value and 0-100 % proportional range of input signal. A classical example of a water treatment process chain is that in which a flowmeter delivers a signal to the Vl 92 which processes it through the proportional function. The thus processed signal is picked up by the self-regulator which converts it into a mechanical movement which, in turn, changes the stroke of the crank mechanism to regulate the flowrate of the metering pump PD. The feedback signal emitted by the self-regulator AR 91, communicates the Vl 92 its actual reading and, consequently the one of the Metering Pump PD, the latter data being visualized on the display.

Display Performance

When acting as a display unit, the Vl 92 is characterized by not having any preset unit, that is, it can be used for any type of measurement by simply resetting the instrument's full scale. For example: for a pH signal coming from a regulating system the relevant unit must be indicated on the sticker, and the instrument must be calibrated for values of 0-14 in correspondence of the 4-20 mA signal. Moreover, the instrument is provided with a 0 100% settable threshold which operates a relay for a n.o./n.c switching to be used as an alarm or basic regulation.

Interface Performance

The interfacing function carried out by Vl 92 consists in decoupling the source of the regulating signal and the self-regulating metering pump through the intervention of a presettable proportionality parameter. For example, in the case of a flowmeter with 4-20 mA output and 0-100 m3/h measuring range and a metering pump which must set itself at 50% of its max. capacity to admit the right amount of reagent into the channel when the flowrate of the latter is 100 m3/h such case, if the flowmeter is directly connected to the self- regulating pump there is obtained that at 100% (20 mA) of channel flowrate the pump capacity is automatically set to 100%. By interconnecting Vl 92 between the flowmeter and the pump it is possible to set the proportion between the flowrate signal and the pump reading which in this case is 50%. In case the input signal drops to a 0, the status of the relay contact is switched. This function can be used either to turn off the pump motor by a contactor or to act as a failure indication when the input signal is preset not to be equal to 0 in any case. A further characteristic of Vl 92 is that of allowing the pump to be manually regulated from the front of the instrument in case of an emergency situation. Vl 92 is provided with a built-in supply unit for Sodi Scientifica flowmeters.

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