In-Place Inclinometer Q&A

Do in-place inclinometer sensors have to be connected? If so, is it necessary to have a rigid gauge tube? Would a fiberglass rod work just as well?

Answer: Some applications require rigid connections between sensors. For example, landslide movements, where shear planes and interupting a smoothly distributed strain pattern at various depths. Detecting and measuring the shear zones are the most important aspects of monitoring these movements. Here a rigid system of connection rods and sensors must be used, particularly when the exact location of the shear is not known. Rigid connections are less necessary when shear planes are not expected and good assumptions about gauge lengths can be made due (i.e. elastic and plastic strains are smoothly distributed). In such cases, discrete sensors that are grouted in place would be acceptable. I think the grouting is necessary because flimsy skids and flexible rods are likely to change position when movement occurs, due to axial compression or tension or interference of cables.

Question: What are the electrical specifications for your EL IPI sensors?

Answer: EL IPI sensors are supplied with an on-board signal contitioning module.

Question: What are the electrical specifications for multiplexed EL IPI sensors?

Answer: Here are the electrical specifications and timing for the multiplexers:

Input power range: 9-15 VDC (12 Vdc nominal)
Digital inputs: High: Minimum 3.5 Vdc Maximum 5.3 Vdc
Low: Minimum 0 Vdc Maximum .5 Vdc

Minimum pulse width (high): 1 milliseconds
Minimum pulse width (low): 1 milliseconds
Minimum Switching time (on): 5 milliseconds
Minimum Switching time (off): 2 milliseconds

Reset and Clock are normally low digital inputs, with an internal 10k pulldown.
Timing is relative to leading edge of pulse.

Power ground and analog ground are normally tied together at the data logger. The Campbell CR10X data logger does this internally.

Description:

Enable/Reset
Low: Disables all sensors, resets counters to 0. Clock inputs are ignored in this state.
High: Enables clock inputs.

Clock

Low: No action
High: First clock enables the Channel A signal output.
Second clock enables Channel T signal output.
Third clock enables Channel B signal output. (Biaxial sensors)
Fourth clock puts Serial MUX in repeater mode.
The fourth and all subsequent clocks are passed on to the next SMUX

Operation:

Reset low turns off all switches, isolating all signal output.
Reset high prepares the first (nearest) sensor to be enabled on the next clock pulse.
Each serial mux responds to 3 clock pulses, then sends subsequent pulses
onward to the next mux in the string.
Muxes respond in the order in which they are physically wired in the string.
To read the 12th sensor in a string of sensors would require a total of 11 * 3 + 1
clock pulses following the reset.

Example:
To read the serial devices, begin with a reset low, then
raise Reset to +5v to enable MUX.

clock Mux1 Mux2 Mux3 ...
1 ch A X X
2 Ch T X X
3 Ch B X X
4 rpt chA X
5 rpt chT X
6 rpt chB X
7 rpt rpt chA
8 rpt rpt chT
9 rpt rpt chB
10 rpt rpt rpt
...

NOTES:

Timing note: Serial Mux can respond to pulse widths as short as 120 microseconds.
1 millisecond is specified for minimum high and low to allow time for
redundant validation, should first validation loop fail due to noise.
There is up to a 5 millisecond delay after clock before the switch turns on.