Electromagnetics - Frequently Asked Questions

  • What is CMD instrument?

  • It is an electromagnetic conductivity meter (EM instrument working at a low induction number) providing calibrated values of apparent conductivity as well as inphase quantity measured with the specified depth range. (Not to be confused with electromagnetic ppt meters working in a wide range of induction numbers without specified depth range.)

  • Is CMD multifrequency instrument?

  • No, it is a multidepth, frequency domain instrument. The selection of working frequency is connected with linearity of the calibration curve according to the distance of magnetic dipoles. To understand it see Short guide for electromagnetics on these web sites.

  • What is the orientation of magnetic dipoles?

  • CMD contains one or more coplanar sensors. This system provides mutual consistency of their individual depth ranges based on the same shape of antenna diagrams. Thus an easier possibility of EM inversion is achieved.

  • Compatibility of control units with probes

  • CMD control unit can operate all single depth and multidepth CMD probes allowing firmware upgrade via internet.

  • EM inversion tools

  • The choice of commercially available software for EM inversion is currently extremely poor. There is only a limited family of 1D EM inversion SW (as IX1D by Interpex) and no available 2D and 3D tool for EM inversion. Given the circumstances we have found a useful replacement for EM 2D and 3D inversions made by 2D and 3D inversion SW for DC methods. In addition, CMD is equipped with 1D in-situ EM inversion which converts individual multidepth measurements into 2 layered model (upper layer and bottom layer conductivities and depth of their border).

  • Depth ranges and method of calibration

  • Each CMD probe has two depth ranges - high depth range with vertical orientation of magnetic dipoles and low depth range with horizontal orientation of magnetic dipoles. A separate calibration for each orientation of the probe is provided.

  • Are the CMDs water resistant?

  • CMD probes are not submersible and are not designed to be exposed to heavy rains, unless covered with special protection.

  • How often should I recalibrate my CMD probe?

  • These are recommended recalibration periods for CMDs:
    CMD-DUO, CMD-4/6, CMD 4, CMD 2: 10 years
    CMD Explorer, CMD Mini Explorer, CMD 1: 5 years
    CMD Tiny, CMD Mini Explorer 6L, special multidepth instruments: 3 years
    For occasional check or a case of probe damage, we recommend to establish your own check measurement point.