top of page

Study the Block Diagram in the Wet-Bath Simulator Manufacturer's Manual

Tip 25: Obtain a copy of the Guth Laboratories, Inc. wet-bath "Model 2100 Simulator Operation Manual" and study the "Model 2100-Block Diagram" at page 13. Notice the "Display Section-34.0C- Multiplexed Display Driver" and "RS-232 Level Converter".

block diagram of electronics
R. v. P. Exhibit 10 at L'Orignal Block Diagram excerpt from Guth 2100 Manufacturer's Manual

These two temperature data output systems are connected to the "8051 Micro Controller". Their source of temperature information appears to be the one micro controller. They do not appear to have sources of temperature information independent of each other. They receive their temperature information from the same source (the Precision Thermistor) and so it is always the same information, except that one display may have two decimal places (the RS232 interface to the 8000C) and the other may have one decimal place (the Guth 2100 display).

But most importantly, neither display appears to have a source of temperature information (a probe independently sensing temperature), separate from the "precision thermistor", the thermostat that (through the micro controller) controls the Guth 2100 heater. NEITHER THE DIGITAL DISPLAY THERMOMETER NOR THE RS232 THERMOMETER APPEAR TO BE INDEPENDENT OF THE HEATER CONTROLLED BY THE "PRECISION THERMISTOR".

It therefore appears that the only reliable method for a Qualified Technician to check the solution temperature, is to manually observe the temperature indicated on the (OPTIONAL) yellow NIST mercury thermometer. It appears that police services who rely entirely on the Guth 2100 digital display or the RS232 interface are not independently checking the simulator temperature. All they are doing, if they rely on the digital display or the RS232 system, is relying on a reading of the thermistor temperature controlling the heater.

If you have information from the manufacturer that contradicts this interpretation of the block diagram or you have a better block diagram of the Guth 2100, please phone the author immediately at 1-877-273-3322 and this blog entry will be corrected accordingly.

Perhaps it is, because the digital display/RS232 display system is not independent of the heater thermistor, that Qualified Technicians are trained, since 2010, "It is recommended that a NIST mercury thermometer is used when using a digital simulator to confirm the display temperature." See blog entry Verification of Digital Thermometer herein.

E-mail dated May 26, 2010
E-mail from Inger Bugyra to CFS scientists May 26, 2010 obtained through FOI application

Please note that many OPP detachments now use a different wet-bath simulator with their Intoxilyzer 8000Cs, the Guth 12V 500. The Guth web site says:

"The Model 12V500 is the first simulator of its kind to incorporate dual temperature probes to independently control and monitor the temperature of the solution."

It appears that Guth has acknowledged the need to improve its simulators so as to incorporate dual temperature probes. The OPP are to be commended for their use of Model 12V500s in many detachments. Other police services who have not yet replaced their Guth 2100 simulators need to learn from the OPP.

It is fairly easy to distinguish the two Guth simulators (2100 and 12V500) when looking at a breath room video. The Guth 2100 looks like this:

Guth 2100 simulator
Photograph of the author's Guth 2100 simulator

An image of a Guth 12V500 can be found at the Guth web site. Note the display reads to two decimal places whereas the Guth 2100 display reads to one decimal place. Strangely, Intoxilyzer Test Records and COBRA data in Ontario read to two decimal places whether the simulator is a Guth 2100 or a Guth 12V500.

Quaere: In jurisdictions where police use a Guth 2100 rather than the newer Guth 12V500, do defence lawyers have an argument that they can produce Interpretation Act "evidence to the contrary" to negate any use of 320.33 by the Crown?

Quaere: How does the OPP verify the calibration of their 12V500 displays/RS232 output to two decimal places? Do they have access during semi-annual periodic inspections to NIST reference thermometers reliable to three decimal places? This is a different issue than reliablility of the simulator heating system to +/- .05 degrees C. Do Intoxilyzer Test Records that show simulator temperatures at two decimal places (eg. 34.00 or 34.02) therefore provide unreliable information to the Court - thus negating the 320.33 presumption?

Recent Posts

See All


bottom of page