Point Measurements

DESIGN PHASE:       measurement
SUB ELEMENT NAME:   point measurements
APPLICABILITY:      all circuits

ACTIVITY:  Make room temperature "point measurements" of the
circuit to verify circuit is working as intended, obtain
preliminary data, and obtain nodal voltages and key branch
currents in each operating mode to compare to computer analysis
outputs under the same operating conditions in order to verify
the computer model before using it for worse case analysis.

Point measurements are made with a multimeter and oscilloscope
(to verify circuit is not oscillating and to measure ripple and
noise if present).  Point measurements consist of:

quiescent.currents (current circuit draws with no load)
power.loss (or efficiency, calculated from power measurements)
drop.out.voltages (main and bias voltage where output goes out of
coffin.corners (worsecase extremes)


Measurements recorded in laboratory notebook for comparison to
specification and computer analysis.


[HEMP] =            engineer hours for point measurements
[HTMP] =            technician hours for point measurements
0.0+                set up time
0.5*                split time between engineer and technician
0.00*               time per point measurement
[NPM]*              number of point measurements in set
[NPS]*              number of sets
[MODE COUNT]        number of circuit operating modes

[NPM] =             number of point measurements in a set
[NNV]+              number of nodal voltages = [NODE COUNT]
[NBC]+              number of branch currents = [INPUT COUNT] +
                    [OUTPUT COUNT] + 2* [TRANSISTOR COUNT] +
                    [DIODE COUNT] + [IC COUNT]
[NQC]+              number of quiescent currents = [INPUT COUNT]
[NIP]+              number of input power measurements =
                     [INPUT COUNT]
[NOP]+              number of output power measurements =
                     [OUTPUT COUNT]
[NPL]+              number of power loss calculations =
                     [INPUT COUNT]+[OUTPUT COUNT]
[NDO]+              number of drop out voltage measurements =
                     [INPUT COUNT]
[NTP]               number of operating mode transition points =
                    [MODE COUNT]-1

[NPS] =             number of point measurement sets
[NWC]+              number of worse case condition sets measured
                     (default = 4)
1.0                 nominal measurement


Time per measurement is estimated as being done by engineer alone
and then time is split between engineer and technician and set up
time is added for both.

The number of worse case condition sets measured [NWC] is the
number of worse case conditions that a set of measurements are to
be made.  The number of coffin corner measurements can quickly
become excessive unless careful judgment is used.  The default
value is 4, and for these 4 worse case settings and nominal, a
complete set of measurements is made for each operating mode.  It
may be desirable to take a partial set of measurements at other
operating points if time allows.

For series regulators, the program can be run for one
or two operating modes, the voltage regulating mode and the
current regulating mode.  

Actually, there are two operating modes, one where the voltage
regulating loop has control and one where the overcurrent loop
has control.  The transition point is where the regulator goes
from normal regulation to overcurrent protection.  The first set
of measurements is usual taken at nominal inputs and full load.
Then the overcurrent transition point is checked and adjusted if
necessary and the short circuit measurements made.  The coffin
corner measurements are then made at no load and just before
entering into current limit.  Input conditions are high line and
associated worse case biases, and low line  and associated worse
case biases.  If any problems occur, adjustments are made.  The
circuit is then checked for overcurrent-mode coffin corners.  The
load points are just after going into current limit and short

Author: Jerrold Foutz, foutz@smpstech.com

Original: Foutz, J., Power Supply Circuit Development Estimating Aid - An Expert System Application, IEEE Applied Power Electronics Conference Record, New Orleans, February 1-5, 1988. Revised 21 February 2001