Analog Devices ADSST-EM-3040 Easy Calibration, Ease of Design, Quadrant and Other Conventions

ADSST-SALEM-3T

EASY CALIBRATION

The ADSST-SALEM-3T chipset has highly advanced calibration routines embedded into the software. Ease of calibration is the key feature in this chipset. By sending specific commands to the ADSST-SALEM-3T chipset, the dc offsets and gains for all volt- age and current channels can be calibrated automatically. Active and reactive power calibration is also available for fine-tuning the errors.

The meter and calibration constants are stored in an external flash memory, and the lock/unlock calibration feature enables protection of the calibration constants. The ability to upgrade the firmware residing in the flash memory makes the meter adaptable to future needs.

EASE OF DESIGN

Designing a complete meter using the ADSST-SALEM-3T is very easy with the ADSST-SALEM-3T-DK developer’s kit. The kit in the UART mode enables a user to evaluate and test the computational element by connecting to a PC, without building the complete hardware.

QUADRANT AND OTHER CONVENTIONS

The metering data computed by the ADSST-SALEM-3T chipset uses the following conventions for various parameters:

•Figure 2 gives the quadrant conventions used by the chipset.

•Import means power delivered from the utility to the user.

EFFECTIVE PHASE COMPENSATION

The ADSST-SALEM-3T chipset employs an algorithm (patent pending) for phase compensation. The ADSST-SALEM-

3T chipset based meter, which is very effective and user friendly, can be calibrated for phase compensation at three current points to cover the complete current range. This also reduces the cost of the end product by reducing the cost of the sensing elements, i.e., current transformers.

•Export means power delivered by the user to the utility.

•Total means total of all three phases.

Import and export are with reference to consumption.

U, I:	Magnitude of voltage and current
P:	Active Power (U × I × cos Φ)
Q:	Reactive Power (U × I × sin Φ)
Φ:	Phase angle from the standpoint of I with respect to U,
	always positive in counterclockwise direction.
Phase U: L1		= 0° Abs
	L2	= 240° Abs
	L3	= 120° Abs

	ACTIVE EXPORT					ACTIVE IMPORT
				(–90° Φ)
		REACTIVE
		SIN Φ = –1		(90° ABS)
			P–Q–	P+Q–			ACTIVE
							CAPACITIVE (LEAD)
		QUADRANT II		QUADRANT I
REACTIVE EXPORT
	ACTIVE						ACTIVE
	COS Φ = –1						COS Φ = +1
	(±180° Φ)				Φ	I	(0° Φ)
	(180° ABS)		IQ				(0° ABS)
REACTIVE IMPORT		QUADRANT III		QUADRANT IV
			P–Q+	P+Q+			ACTIVE
							INDUCTIVE (LAG)
		REACTIVE		(+90° Φ)
		SIN Φ = +1		(270° ABS)
			L1, L2, L3				03738-0-002

Figure 2. Quadrant Conventions

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