Sencore FE149 - Page 12

on the lower scale of the meter. If the battery indicates below the green area, re-
charge the battery or calibrate the FE149 using AC power). Set the front panel
ZERO ADJ fully clockwise and adjust R21, the DC balance control, for a reading of
.3 оп the .5 scale ofthe meter. See Figure 2 for the location of R21 and the other
calibration controls. Set the front panel ZERO ADJ for zero on the left side of the
meter. Depress alternately the plus and minus DC volts buttons on the Function
switch. The meter needle should move only slightly, if at all.
AC BALANCE: After setting the DC balance, depress the AC volts button and adjust
R22, the AC balance control for a zero indication onthe left side of the meter. De-
pressing the plus DC volts and AC volts buttons alternately should produce very little
meter deflection.
DC VOLTS: The DC voltage ranges can be calibrated using an accurate .5 volt
source and adjusting R10 located directly behind the plus DC volts push button for
а full scale meter deflection. Ifan accurate .5 volt source is notavailable, a fresh
1.5 volt battery may be used. Depress the plus DC volts Function button and the
1.5 voltRange button. Connect the battery to the input of the FE149 and adjust R
for a reading of 1.55 volts on the 1.5 volt scale of the meter.
AC VOLTS: To calibrate the ACranges, anaccurate .5 volts RMSsine wave is rec-
ommended. With the AC voltage applied, R59, found directly behind the AC volts
push button is adjusted for a full scale meter deflection on the .5 volt range. If an
accurate AC voltage source is notavailable, you may use a 12.6 volt filament trans-
former or the 117 volt AC line. Depress the proper range button, 15 if you are
using а 12.6 volt source or the 150 volt range if you are using the AC line and adjust
R59 for the proper meter indication.
AC CURRENT: The AC current ranges of the FE149 canbe calibrated using a known
source of AC current. Ап alternate method is to apply a .3 volts RMS AC voltage
from a low impedance source to the input with the FE149 set up for 150 microamp
ACcurrentrange. A .3 volt signal will give a full scale deflection of 150 microamps
on the meter. R12, located directly behind the AC current Function button is used
to adjust the AC current ranges of the FE149. To obtainthe .3 volt RMS AC signal
use the circuit below. The potis adjusted until the FE149 reads .3 volts on the AC
scaleof the meter. Thendepress the AC current Function button and the 150 micro-
amp range button and adjust R12 for 150 microamp reading on the meter.
LOW OHMS CAL:
Figure 3
Battery impedance, switch апа battery contact resistance, resistance of the test leads
etc., allaffect meter accuracy onlow ohms measurement. The ЕЕ149 has a special
adjustment, the low ohms cal, which is used to calibrate the mid scale of the low
ohms range. Before this control is reset, a new battery should be installed. Set
the function switch in OHMS and the RANGE switch іп КХІ position. Adjust the met
fora full scale deflectionor 0 (zero) ohms with the ohms adjustcontrol. Unshort th®
leads to be sure they return to zero at the left hand side of the meter. Now, using
a precision 6 ohms resistor applied to the input, adjust the low ohms cal (found on
the range switch board on the lower right hand corner) until the meter reads 6. If
а 6 ohms resistor is notavailable, a 5ohm unitwill work. Тһе tolerance of the re-
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