Power meters provide an early warning of thermal overload by monitoring the power consumption in 'high reliability' systems. Power monitoring is especially suitable for systems in which the load voltage and current are both variable such as industrial heating and motor controllers.
Such a power meter/controller (Figure 1) is based on the principle that power equals the product of current and voltage. Its typical accuracy is better than 1%.
Figure 1. This power meter, whose output voltage is proportional to load power, achieves ±1% accuracy
Method
A current sensor (U2) measures output current, and a four-quadrant analog voltage multiplier (U1 and U3) generates the product of output voltage and current. An optional unity-gain inverter (U4) inverts the inverted multiplier output. This power meter is most accurate for multiplier inputs (J1 and J2) between 3 V and 15 V.
Choose the current-sense resistor, RSENSE, as follows:
RSENSE (Ω) = 1/P (W)
where RSENSE is in Ω and P is the output power in W. If power delivery to the load is 10 W, for instance, choose RSENSE = 0,1 Ω.
The Figure 1 circuit, with a 0,1 Ω sense resistor, has a unity-gain transfer function in which the output voltage is proportional to load power. For instance, the output voltage is 10 V when the load power is 10 W. To change the gain transfer function, change the sense resistor as follows: Gain = 10 RSENSE.
Figure 2 compares power-measurement error with load power for the Figure 1 circuit. Note that the accuracy is better than ±1% for load power in the 3 W to 14 W range.
Figure 2. The ‘Power-measurement error vs power’ graph shows measured power has better than ±1% accuracy for power levels between 3 and 14 W
Calibration
For proper operation, the analog multiplier must first be calibrated according to the following procedure (which also appears in Motorola's MC1495 data sheet). To calibrate the multiplier, remove jumper J1 (X input) and J2 (Y input), and use the following procedures:
(1) X-input offset adjustment: Connect a 1,0 kHz, 5 VP-P sinewave to the Y input, and connect the X input to ground. Using an oscilloscope to monitor the output, adjust RX for an AC null (zero amplitude) in the sinewave.
(2) Y-input offset adjustment: Connect a 1, 0 kHz, 5 VP-P sinewave to the X input, and connect the Y input to ground. Using an oscilloscope to monitor the output, adjust RY for AC null (zero amplitude) in the sinewave.
(3) Output offset adjustment: Connect both X and Y inputs to ground. Adjust ROUT until the output DC voltage is zero.
(4) Scale factor (Gain): Connect both X and Y inputs to 10 V d.c. Adjust RSCALE until the output voltage is 10 V d.c.
IMU with dual-sensing capability EBV Electrolink
Analogue, Mixed Signal, LSI
ST’s 6-axis inertial measurement unit integrates a dual accelerometer up to 320g and embedded AI for activity tracking and high-impact sensing.
Read more...Plural data converter series
Analogue, Mixed Signal, LSI
Silanna Semiconductor has announced the launch of Plural, a new generation of data converters for customers eager to find a more available, affordable, high-performance alternative to existing brands.
Read more...Precision JFET op-amp Altron Arrow
Analogue, Mixed Signal, LSI
The specifications of the ADA4620 make it optimal as a front-end amplifier in a data-acquisition system, or for a TIA circuit with high input impedance.
Read more...A new era in modular I/O solutions Rugged Interconnect Technologies
Analogue, Mixed Signal, LSI
Aerospace and defence system designers are demanding scalable and high-performance I/O solutions and while traditional mezzanine standards have proven reliable, they often fall short of meeting modern bandwidth, size, and flexibility requirements.
Read more...High voltage instrument op-amp iCorp Technologies
Analogue, Mixed Signal, LSI
The SGM621B is a high accuracy, high voltage instrumentation amplifier, which is designed to set any gain from 1 to 10 000 with one external resistor.
Read more...High-speed SAR ADC simplifies design Altron Arrow
Analogue, Mixed Signal, LSI
The ADI AD4080 simplifies data converter integration by integrating a low drift reference buffer, low dropout regulators and a 16K result data FIFO buffer.
Read more...2-wire quad voltage output DAC Altron Arrow
Analogue, Mixed Signal, LSI
The DAC has a 2-wire serial interface that operates at clock rates up to 400 kHz, and this interface is SMBus compatible, allowing multiple devices to be placed on the same bus.
Read more...Dual-channel ADC for RF applications RFiber Solutions
Analogue, Mixed Signal, LSI
The ARF0471 from Advanced RF is a dual-channel, 14-bit, 3 GSPS ADC, which features an on-chip buffer and sample-and-hold circuit.
printer friendly version