Friday, November 6, 2009

Level measurement by Dp transmitter

Level measurement using DP transmitter is common to use, even can be called as a first choise for the level transmitter, but much cheaper than type2 as displacer level transmitter, radar wave, etc., in addition to easier installation.

DP Transmitter principle itself is hydostatik pressure from the formula:
P = pgh

To open the tank, for the high P diconnectkan to the bottom of the tank, while for P is low, just enough atm, this is because:
Phigh = pgh + atm, Plow = atm
So to compensate for atm, DP = pgh + atm-atm
Obtained h.

Meanwhile, close to the tank, just like an open tank, but for low P diconnectkan to the top of the tank, this is to compensate for the gas pressure from the tank:
thus becomes DP = pgh + PGAS-PGAS, so get h.

At the measurement level using DP, we must know the property (P or can also SG) is fluid.

Closed tank to have two kinds of installations are:
1. Dry Leg: where to P low, the transmitter direct contact with the fluid, in this case the fluid is a gas
2. Wet Leg: where to P low, the transmitter given the different media such as fluid (glycol / silicone oil / water-common) for compensation from the condensation of the fluid media measured (using diapragm) or because a particular case (such as a corrosive gas fluid)

Thursday, November 5, 2009

Basic of calibration

To find a measure of best quality and quantity, process control is required. The value must be obtained from the gauge mounted on the process. Instrument must be accurate. Measure requires some setting of variables such as: range, zero, span, variable settings are needed to detect, manage and control the error, linearity, accuracy.
1. Process Variables
Process variable is the amount of physical or chemical quantities because of the influence of the process. Pressure, temperature, flow and level is the physical variables, whereas the oxygen content and pH values are chemical variables.
2. Range
Range is the boundary between the lowest value to highest value. For example, a physical variable of a process of value between 3 to 10 bars then, instruments used must have the highest value and the ability to measure the indicator value above 10 bar and the lowest value of 3 bars
3. Zero
Zero shows the lowest signal from the input or output and does not interpret the value of 0 (nil). A transmitter with the input range = 0 to 10 bar, output = 4 to 20 ma. So 4ma output value and input value is 0 bar zero value.
4. "Span"
The difference between the lowest and highest value is called "span", 0 to 10 bar has a value of span = 10 bar. 4 to 20mA has a span value = 16.
5. Error
The difference with the actual process value indication value measure is the actual process error.Ketika value and 5 bar gauge shows the mean error 5.2bar = 0.2bar
6. Linearity
In full-scale output than the input point as a point of readability measurement Linearity
input and output 0% 0%
input and output 25% 25%
input and output 50% 50%
input and output 75% 85%
input and output 100% 100% then the instrument is said to be non-linear
7. Accuracy
Measurement error value of the real value of the scala a full percentage accuracy values describing a tool ukur.contoh 1%, 2% is usually written on the gauge