UFI Model 2994D THRIM™
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 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, deltaR 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. A wall-mount transformer now supplies power, so we have augmented subject isolation with an isolation barrier between the incoming DC power and the rest of the circuitry.
The plastic case (shown in the picture at top) is new for 2004, and can be configured for either rack mounting or desk top. Input connectors are now the robust, easy-to-use Lemo 1B type. The earlier BNC output connectors have been supplemented with high density arrays, ready to mate with conventional A-to-D inputs on downstream instruments.
Typical channel controls for a THRIM
2994D THRIM specifications
Inputs
- 1, 2, 3, or 4 channels of impedance sensing
- Input impedance: 10 KOhms differential
- Rugged Lemo 1B 4-pin input jacks
Functional details
- 51.2 KHz excitation frequency generator
- One-mA constant-current drive excitation
- Crystal controlled for long-term stability
- DeltaR gain: 20, 50, 100, 200, 500, and 1,000 milliohms per volt
Outputs
- LCD display of Ro or Xc (switch selectable)
- 0-199 or 0-1999 LCD range (switch selectable)
- Ro, Xc, deltaR, and dR/dt outputs for each channel
- deltaR output time constant: 1 second
- BNC output connectors standard (other connectors available)
Power supply and mechanical
- Wall-mount transformer standard; battery-power optional
- Black ABS plastic rack-mount or desktop case
- Size: 17" x 5.1" x 8" (430mm x 130mm x 205mm)
Options
- Optional 12-bit A-to-D capabilitity
- Optional ECG amplifier
- Optional transducer-based respiration amplifier
- Additional signal conditioning options are available