Environmental Measurements

DESIGN PHASE:       measurement
SUB ELEMENT NAME:   environmental measurements
VARIABLE NAME:      [HEMOVEN]
DATE:               REVISION LETTER:    REVISION DATE:  
APPLICABILITY:      all circuits

ACTIVITY:  Determine survivability, stability*, worse case
performance, temperature coefficients of circuit, and take PARD
photo over the specified temperature range.

OUTPUT:  Measurements in laboratory notebook for comparison to
specifications and analysis.

ALGORITHM:

[HEMOVEN] =              engineer hours for environmental measurement
[HTMOVEN] =              technician hours for environmental measurement
0.0+                     set up time
0.0*                     time per stabilized temperature
(1+INT(1+
([UTEMP]-[LTEMP])/25))   number of temperature measurements

[UTEMP]                  upper operating temperature extreme in
                         degrees C
[LTEMP]                  lower operating temperature extreme in
                         degrees C

DISCUSSION:
Test Cases:

-55C to 125C (-55,-25,0,25,50,75,100,125) 8 = 8 ok
0 to 70C (0,25,50,70) 4 = 4 ok
-25 to 70C (-25,0,25,50,70) 5 = 4, estimates one too low.

Algorithm not exact but probably ok.

* A good stability screen for regulators with feedback loops is
to apply a square wave to the reference input and observe the
closed loop response as as load is varied for each line voltage
condition at each temperature.  A tendency for instability often
shows up as an underdamped ringing response or oscillation on the
output.  The frequency of ringing, if any, may vary with
conditions and should be recorded or photographed. For more 
details see Power Supply Instability.

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