5-15 Table 5-1.—Front Panel Controls and Connectors—Continued 8, 13 AC/DC These control the selection of ac or dc coupling for the input signal. When the input amplifier control switch (No. 18) is in COM A, channel B coupling is determined by setting of channel A coupling switch. 9, 12 ATTEN switches These select the attenuation of the input signal. The signal amplitude is reduced by 10 in ×10 and by 100 in ×100. When the input amplifier control switch (No. 18) is in COM A, the channel B attenuation is determined by the channel A attenuation switch. 10, 11 INPUT A and B These are the input BNC connectors for channels A and B. 15, 20 LEVEL A/B These controls are used in conjunction with the ATTEN (Nos. 9, 12) to select the voltage at which triggering will occur. With X1 attenuator selected, the level is variable at ±2.5 volts, and ×100 at ±250 volts. 16, 21 Channel A and B triggering lights The light will blink for the associated channel when triggering is occurring. When the light is off, the input signal is below triggering level and on when the signal is above triggering level. 17, 19 Channel A and B SLOPE switch These switches control the selection of triggering on either the positive or negative slope of the input signal. 18 COM A/SEP This is the input amplifier control switch that selects independent operation of channels A and B in SEP (separate) position. When in COM A (common A) position, the signal at A is also applied to channel B; this disconnects the channel B input circuitry. Channel B coupling and attenuation are then determined by the channel A setting. 22 OVERLOAD This indicator will flash on and off if more than 5 volts is applied to channel C input. 23 K, S, M, n, and Hz These will light up to show the appropriate units multiplier of the measurement being taken. 24 LED display This is a nine-digit LED display that shows the numerical measurement taken. NO. NAME DESCRIPTION 25 OVFL This indicates an overflow of one or more of the most significant digits (leftmost from the decimal point) are not displayed. 26 RMT Lights when the unit is in remote operation. 27 GATE Lights when the counter's main gate is open and a measurement is in progress. Table 5-2.—Rear-Panel Controls and Connectors NO. NAME FUNCTION 1 VOLTAGE SELECTOR Used to select 115 or 230 volt operation. 2 LINE FUSE This requires the insertion of a 2.0 amp fuse for 115 volt or 1.0 amp fuse for 230 volt operation. 3 Input ac connector Used to connect the input ac to the unit. 4 ARM When this switch is in the OFF position, the counter is armed by the signal that is selected for measurement. In the ON position, the measurement is armed by an input other than the input being measured. 5 EXT OSC This input connector allows a separate outside signal to be used for the time base. 6 1 MHz OUT and 10 MHz OUT These connectors allow an internal oscillator signal to be used externally when connected. 7 GATE/MARKER OUT Applies a high to the output when the main gate is open. 8 HP-IB This is an interface bus connector that allows the unit to receive programming instructions.