UFI Model 2994D THRIM™

Tetra-polar High Resolution Impedance Meter

The 2994D THRIM is a Tetra-polar High Resolution Impedance Measurement device, designed for use with human subjects. Subject connection is via electrodes placed on the skin.

A single, crystal controlled, constant current "Excitation" generation block supplies the necessary drive signal, and also synchronizes the overall demodulation process for individual channels.

Multiple "Demodulation" or measurement channels sense and supply 4 specific Impedance values (Ro, Xc, deltaRo, dRo/dt) from each of the up to 4 subject segments located between the two Drive points.

The use of a built-in "3 Port Isolation" scheme enhances subject safety. Power for the 2994D THRIM can be supplied by 6 ea. "C" alkaline batteries, or by the supplied external DC power supply.

2994D THRIM Development

The first steps toward the UFI THRIM™ (Tetra-polar High Resolution Impedance Meter) were for a human-subject centrifuge project, in 1982. This instrument measured impedance in the body to quantify fluid shifts under acceleration.

The THRIM design was expanded into a desk-top, multi-channel impedance instrument in 1985. Using built-in constant-current excitation, this instrument supplied complex impedance (Ro and Xc) as well as pulsatile (deltaR and dR/dt) signal outputs for each channel. A front panel LCD for each channel displayed Ro or Xc using one of two different ranges (0-199 or 0- 1,999). A Pulsatile Size Control adjusted the deltaRo output. This analog-only design supported up to four channels.

UFI redesigned the THRIM in 1998 to use a more stable "digital synthesis" impedance measurement technique. Crystal-locked stability was integral to this revised architecture, which also featured a much-reduced parts count and 9V battery power. Like the 1985 design, the 1998 version featured four outputs for each channel (Ro, Xc, deltaRo and dR/dt) and adjustable pulsatile size control.

We revised the THRIM yet again in 2004, this time for another centrifuge project. In response to numerous customer requests, UFI added subject isolation to all THRIM outputs. An in-line transformer or batteries now supply power, so we have augmented subject isolation with an isolation barrier between the incoming DC power and the rest of the THRIM circuitry.

The plastic case (shown in the picture at top) is also new for 2004, and can be configured for either rack mounting or desk top use. Input connectors are now the robust, easy-to-use Lemo 1B type. The BNC output connectors are still standard, but high density connectors are available as an option.

2994D THRIM specifications


Functional details


Power supply and mechanical


Typical channel controls for a THRIM

Some THRIM distinctives

One of our colleagues, Dr. Les Montgomery, has substantial experience, both with bio-impedance, and with the use of our THRIM. He kindly offered the following list of THRIM distinctives!

THRIM Publications

This is a sampling of recent publications that include THRIM use.

THRIM Instruction Manual

This is a representative Instruction Manual for a THRIM system. Carefully read this manual through if you are thinking about purchasing a THRIM.

Product Families:
Bioamps/signal conditioners
Ambulatory data loggers
Hot Flash Recording
BAERCOM™ hearing tester
PC-based instruments
Multi-subject systems
Test instruments