Real-Time Dynamic Compensation for Static Pressure Effects

Performance under pressure - DP Transmitter Static pressure (SP) is applied equally to both the high-pressure side and the low-pressure side of a DP transmitter and can vary the linear

Accurate measurement is vital to efficient plant operation and plant characteristics of the DP signal output. The effect is called Staticsafety. When selecting a transmitter, a lot of attention is paid to the Pressure Effect . This characteristic has both Zero Effect and Reference Accuracy noted in supplier's specification documents. Span Effect components.Reference Accuracy gets its name because the accuracy is basedon a set of reference conditions. The reference conditions dictatea certain temperature, humidity, and static pressure for the Reference Accuracy to be measured in a laboratory setting. In the real world, DP Transmitters are rarely installed in a laboratory and never under the rigid confines of those reference conditions; therefore,Real-world Performance (RWP) is always worse than the Reference Accuracy. To improve RWP, all smart transmitters on the market SP Effectcompensate for variations in temperature; but, Yokogawa's sensorused in the EJA-A series, EJX-A series, and EJX-B series is unique inthe market place because it can compensate for effects in static pressure change as well. This ability is referred to 0% 100%Real-time Dynamic Compensation .

Static Pressure Effects SP = 100

Using differential transmitters to measure flow and tank level are examples of applications where variations in static pressure can effect 100 100 100 200the differential pressure readings of a transmitter. 0%

SP = 0

0 0 0 1000%

PTN1011.003a

To quantify the impact, Real-world Performance (RWP) can be calculated per published specifications and process conditions. RWP isa combined error of Reference Accuracy (E1), Temperature Effect (E2),Static Pressure Zero Effect (E3) and Static Pressure Span Effect (E4).

Competitors state that the static pressure zero effect (E3) can bePTN1011.001a zeroed at line static pressure during the setup of the transmitter.

In many flow measurements or process level applications, staticpressure is not maintained at a constant value. As operational conditions change, the static pressure exerted on the DP transmittervaries. Hence, the static pressure zero effect (E3) cannot always be cancelled by zeroing at line static pressure during setup. This effectcannot be neglected when evaluating the real-world performance.

Yokogawa's Full Dynamic Compensation

Yokogawa's silicon resonant sensor is a true multi-sensing platform.It can measure differential pressure, static pressure, and temperaturein one compact sensor chip. This multi-sensing sensor allowsthe transmitter to use correction coefficients stored in the sensor's ROM to compensate for fluctuations in static pressure and temperature to reduce the static pressure and temperature effects.The correction coefficients are unique to each sensor and are

PTN1011.002a generated at the factory through rigorous testing (See Figure 1).Page 1 of 2

LH.080111.01a PTN-1011 1st Edition 08/2011

LH.012711.a

Static Pressure Zero and Span Effect

Input (DP)

ERRO

R (%

)

Flow Measurement

ΔP ≈ Flow²

Level Measurement

ΔP ≈ Process Level

E3: SP Zero Effect

E4: SP Span Effect

100%

100%

Field Instruments

www.yokogawa.com/us

Alternate Sensor Technology

Capacitive sensor technology used in the marketplace is not capableof multi-sensing. It can only measure differential pressure. The DPtransmitters using this type of technology incorporate a resistive temperature sensor near the capacitive sensor to compensate for temperature fluctuations; but, they do not add a separate sensor to measure static pressure for static pressure fluctuations. Therefore, these transmitters are not capable of minimizing the static pressure effect (See Figure 2).

Figure 1 Yokogawa's Multi-sensing Resonant Sensor Technology

Transmitter

SiliconResonant

Sensor

Figure 2 Capacitive Sensor Technology PTN1011.003a

Transmitter

CapacitiveSensor

RTD

Not measured Static Pressure is not measured; therefore it is not compensated for.PTN1011.004a

Figure 3 Comparison of Real-world Performance

Conclusion

Even in high static pressure applications, Yokogawa's EJA-A / EJX-A / EJX-B series dramatically reduces the static pressure effects and providessuperior total performance. Using the published specifications, the Real-world Performance can be calculated for comparative estimates (See Figure 3). Note that the Reference Accuracy is the smallest component of the calculations.

E1: Reference Accuracy Calibrated Span: 0 to 1500 inH ₂OE2: Temperature Effect Static Pressure: 1,200 psigE3: Static Pressure Zero Effect PTN1011.005a

E4: Static Pressure Span Effect Page 2 of 2

LH.080111.01a PTN-1011 1st Edition 08/2011

Process

Process

www.yokogawa.com/us

Field Instruments

Correction Coefficients

Dynamic CompensationTemperature Effect

&Static Pressure Effect

Primary Variable:Dynamic Compensated

DP Signal(4 to 20 mA)

Differential Pressure

Differential Pressure

Temperature Temperature

Static Pressure Static Pressure

Differential Pressure

Temperature

Static Pressure

Differential Pressure

Temperature Temperature Correction Coefficients

Temperature EffectCompensation

Digital /AnalogConversion

Secondary Variable:Static Pressure

(Digital Protocol)

Third Variable:Capsule Temperature

(Digital Protocol)

Digital /AnalogConversion

Analog /DigitalConversion

Primary Variable:Temperature Compensated

DP Signal(4 to 20 mA)

Secondary Variable:Temperature

(Digital Protocol)

EJX110A

EJA110A

CapacitiveSensor

Transmitter

RWP = E1+E2+E3+E4

0.0% 0.5% 1.0% 1.5% 2.0% 2.5%