TM 9-4935-481-14-1
C2
(i) Operational amplifier AR6 and associated components form a voltage comparator which operates in an
(d) Operational amplifier AR3 and associated components form a voltage comparator. Zener diode VR1 limits
identical manner as the comparator described above.
the output voltage of AR3 to approximately +3 Vdc for positive outputs, and to approximately -0.7 Vdc for negative outputs.
The reference voltage is applied to the inverting input of AR3 through the 10K resistor (R12). The input voltage is applied to
(j) The purpose of capacitors C12, C15, C18 and C21 is to prevent oscillations in operational amplifiers AR3
the same inverting input through another 10K resistor (R11). This type of comparator requires that the reference voltage is of
through AR6, respectively.
the same amplitude but opposite polarity to the voltage limit which it detects. If the input voltage rides below or above -5 Vdc,
the reference voltage must be +5 Vdc. The polarity of the output voltage of the comparator is opposite to the polarity of the
(k) Relays K1 through K11 have control input at pin 9. The 2K ohm resistor at this input limits the control current.
algebraic sum of the input voltage and the reference voltage, e.g. if the input voltage is -5.05 Vdc, and the reference voltage
(l) The voltage required at the input of the current limiting resistor to energize the relay is from +1.2 Vdc to +5.5
is +5.00 Vdc, then the algebraic sum is (-5.05)+(5.00) = -0.05 which is negative. Therefore, the comparator output will be
Vdc.
positive (approx. +3 Vdc). Due to the input offset error voltage of AR3, the comparator output may not switch at this exact
point but will switch within + 25 mVdc. The purpose of resistor R13 is to minimize this input offset error.
(m) +5 Vdc is applied through four external 3K resistors individually connected to pins 29, 12, 51 and 54 on
connector P1. Each of these pins is internally connected to a separate relay circuit capable of selecting various resistors
(e) Operational amplifier AR5 and associated components form a voltage comparator which operates in an
whose opposite ends are tied together in groups of three and brought out on P1 connector where they are externally
identical manner as the comparator described above.
grounded. The external 3K resistor together with the internal resistor selected by the relay circuit, form a two-resistor voltage
(f) Operational amplifier AR4 and associated components form a voltage comparator. The reference voltage is
divider. By measuring the output voltage of these voltage dividers the selected resistor values are verified.
applied to the inverting input of AR4 through the 10KK resistor (R15), and the input voltage is applied to the same input
(n) For testing, the input at P1-1 is connected to +5V and the outputs at pins 7, 8, 9 and 10 are individually
through the 8K resistor (R14). Because the two resistors (R15 and R14) are not equal, the relationship between the reference
connected through a load resistor to ground. By measuring the voltages at pins 7, 8, 9 and 10 the resistances of the internal
voltage (at P1-56) and the required limit voltage is different than for AR3 and AR5. The new relationship is expressed below.
resistors are verified. The measured voltages will be as specified in the test procedure when the internal resistances are
Vlimit = -(R14 R15) Vref
correct.
Substituting actual values into the right side of the equation, Vlimit is found to be -4 Vdc as shown below.
(o) The resistance network between pin 2, and pins 3, 4, 5 and 6 is identical to the network just described and is
tested in the same manner.
Vlimit = [8(K) 10(K)] 5V
(p) Z1 and Z2 are lamp drivers. Their pin function is listed in table 3-1.2..
Vlimit = -4 Vdc
(q) Capacitors C22 and C23 slow down the output voltage rise and fall times of Z1 and Z2. The outputs of lamp
(g) When the input voltage is more negative than -4 Vdc (e.g. -4.03 Vdc), the output of this comparator will be
drivers are loaded by connecting 2.7K resistors, one to P1-20 and the other to P1-22.
approximately +3 Vdc, but when the input volt- age is less negative than -4 Vdc (e.g. -3.95 Vdc), the output of this
comparator will be approximately -0.7 Vdc.
(r) When both inputs (pins 2 and 3 on lamp drivers) are +2.0 Vdc or higher, the output will be +24 1 Vdc.
When either one or both inputs are +0.8V or less, the output voltage will be from -0.5 to +0.5 Vdc.
(h) Due to the input offset error voltage of AR4, there may be a slight difference between the nominal limit
voltage (-4.000 Vdc) and the actual limit voltage, but this difference should not exceed 20 mVdc. The purpose of resistor
R16 is to minimize this error.
3-30.13
