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We have a flow transmitter and it is
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heartbased smart flow transmitter. It is
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configured with 0 to 100 m cube per hour
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range. It supports output 4 to 20 millia
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basin signal. We have a DCS system
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distributed control system. Now this DCS
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system is connected with this instrument
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using two wires. This is the positive
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wire and this is the negative. DCS
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provides 24 volts DC power supply to the
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failed instrument. This flow transmitter
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measures the flow in a pipeline. Let's
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say for example the flow is 0 m cube per
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hour. There is no flow at all. So the
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transmitter regulates the loop current
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accordingly as per the measured flow
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rate. What is the signal range? 4 to 20
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milliamp signal. The four represents
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lower range value. The 20 represents
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upper range value. Right now the flow is
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zero. Then this flow transmitter
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regulates the loop current to the 4
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See the flow transmitter sending 4
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The DCS measures this loop current and
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then displays to the operator. So on the
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operator computer it is displaying 0 m
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cube per hour. So this is the basic
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concept for a 4 to 20 millia based
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instrument which is configured in a DCS
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system. Let's say the flow increased to
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25 m cube per hour. Again the
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transmitter measures this flow rate and
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updates the loop current accordingly.
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Now the transmitter sending 8 miampere
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to the DCS system. The DCS receives this
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8 milliampere and the DCS is already
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configured with the flow transmitter
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details. For example, the transmitter's
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range is 0 to 100 m cube per hour and
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its equivalent signal is 4 to 20
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miampere signal. Accordingly, the DCS
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converts this measured milliampere into
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the equivalent flow rate and then
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displays onto the computer graphics.
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Say the flow is increased to 50 m cube
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per hour. Again transmitter sends 12
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milliampere signal to the DCS system.
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The DCS converts this 12 milliampere
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into equivalent flow rate and displays
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50 m cube per hour in the computer
