ENDEVCO MODEL 136 DC AMPLIFIER
INSTRUCTION MANUAL
IM136
Page 15
2.4.8
Low Pass Filter
This function selection provides for enabling or disabling the built-in 4-pole Butterworth Low
Pass filter (set by header module 31875). The following messages will be shown sequentially
on the LED display each time the up-down EDIT keys are pressed: (1) “OFF”, and (2)
“XX.XX”.
1. "OFF": Low-pass filter disabled.
2. "XX.XX": Low-pass filter enabled. XX.XX represents the corner frequency in kHz.
The “Function LED” corresponding to the Low-Pass Filter function will remain OFF during the
normal mode of operation if the user selected the “OFF” setting (filter disabled). The function
LED will remain ON if the low-pass filter was enabled by selecting the “XX.XX” setting. XX.XX
could be a value from 0.01 (10 Hz) to 80.00 (80 kHz). The unit displays the actual corner
frequency in each channel by reading an ID Voltage (VID) set by the header module that sets
the -3dB corner frequency of the low-pass filter. VID ranges from 0 to 2 VDC. The unit uses
the table shown in section 10.0 to convert the ID Voltage into the corner frequency (in Hz).
2.4.9
Auto-Zero
This function selection provides for auto zeroing the DC output voltage. The following
messages will be shown sequentially on the LED display each time the up-down EDIT keys
are pressed: (1) “OFF”, and (2) “ON”.
1.
"OFF": The unit sets all of the internal DC offset adjustments to neutral.
2.
"On": The unit sets the DC output voltage to zero to within ±10 mVDC (zero will
depend on the DC voltage imbalance present at the input of the amplifier). If the unit is unable
to set the DC output voltage to zero, the setting will revert back to “OFF”. This setting will
change to “OFF” if Auto-Zero is set to “On” and the user makes a change in any of the
following functions: Excitation Voltage, Sensor Sensitivity, Output Scaling, and Low Pass
Filter.
3.
"Auto": The unit sets the DC output voltage to zero to within ±10 mVDC (zero will
depend on the DC voltage imbalance present at the input of the amplifier). If the unit is unable
to set the DC output voltage to zero, the setting will revert back to “OFF”. If Auto-Zero is set to
“Auto” and the user makes a change in any of the following functions: Excitation Voltage,
Sensor Sensitivity, Output Scaling, and Low Pass Filter, then the unit will first set Auto-Zero to
“OFF” before executing the change setting of the function. The setting will be set back to
“Auto” after the user presses the “Select Function” key to select the next function.
The “Function LED” corresponding to the Auto-Zero function will remain OFF during the
normal mode of operation if the user selected the “OFF” setting. The function LED will remain
ON if the Auto-Zero function was set to the “On” or “Auto” setting.
2.4.10
Shunt Calibration
This function selection provides for connecting the shunt calibration resistor installed in the
input connector to either the positive (PSEN+) or negative (PSEN-) terminals. The choices
are:
1. "OFF": The shunt calibration resistor is disconnected from the sensor.
2. "RSH": The shunt calibration resistor is connected to the PSEN+ line.
3. "RSH-": The shunt calibration resistor is connected to the PSEN- line.
The “Function LED” corresponding to the Shunt Calibration function will remain OFF during
the normal mode of operation if the user selected the “OFF” setting. The function LED will
remain ON if the Shunt Calibration was enabled by selecting any of the other settings.