The first step will be to assemble the equipment that you will need to record the response pulses and then get the calbox settings set correctly for the type of sensor being used.

• Reftek DAS (we developed the method using the 16 bit input). Potentially other recorders would work as well, as long as the output could be converted to SAC format.
• Battery to power the reftek
• Response Calibration switch box
• Sensor(s) to calibrate
• Sensor cable, terminated in U77/U connector to mate with response cal box
• Power cables for reftek
• One high quality digital multimeter (to get accurate current measurements).
• banana clip leads for multimeter to connect it to cal box.
• Three connector cal box cable to connect to cal box, reftek comm port and reftek input connector.
• Palmtop computer or other Reftek interface device to program and run monitor function on DAS.

Next we want to establish the correct settings for the cal box. Usually, I like to make sure that the sensors I am calibrating are grouped together by type (Do a bunch of sensors with same response characteristics together). The software is designed so that the user can minimize input if all sensors are same type. More on this later when you see how the software works. Level one of the sensors for the group. Use the cal box and the monitor function of the reftek to look at the pulses on the monitor window. Adjust the Rext value using the rotating switch on the cal box. Raising the resistance value lowers the current and therefore the amplitude of the pulse. You want to find a setting that gives good signal to noise ratio but doesn't approach either the sensor input maximum or the stops of the sensor. To see where the sensor stops are, you would run pulses at different Rext settings (starting high and going towards lower settings) making note of the amplitude at each of those settings. When the current continues to increase, but the amplitude is roughly the same, then you have hit the stops. I often like to try to find an Rext setting that yields an amplitude of about half of the amplitude seen when the sensor hits the stops. This procedure should be done in both the positive and negative directions to make sure that it is about the same.

The next step is to record the response pulses. You will want to program a Reftek 16 bit DAS to record channel 1 only with an externally triggered stream (EXT) that records for about 5-8 seconds with a .5 to 1 second pretrigger length. Since the sequence in which the tech releases the mass and starts the record controls the timing, the settings may vary by user. Be aware that you want at least 1/4 of a second of prepulse silence for each record. I like to have a one second preevent. That way I have about 3/4 of a second after releasing the mass to trigger the DAS. Sample rate should be about 200 or 250 sps.

• Make the cable connections, sensor, reftek comm, reftek input.
• Set resistor array - directly if settings are known. Use Reftek monitor function and geophone pulses otherwise to get good setting. You want a large enough pulse so you get very little noise on the pulse, but small enough so it doesn't saturate the DAS input.
• Start acquisition on DAS (F4-4).
• Move polarity switch to P (positive) position.
• Move cal switch to charge position
• Wait several seconds for sensor mass to settle.
• Move cal switch to release position.
• Trigger DAS (quickly enough so that beginning of pulse is no closer than 1/4 second to beginning of file).
• Move polarity switch to N (negative) position.
• Repeat above steps.