ICL is the official representative of ThermoProbe for Florida, Georgia, Puerto Rico and the Caribbean area – for sales, repairs, calibration, and replacement parts.

Recalibration of your ThermoProbe thermometer is necessary :

• Once each year at least (per API Chapter 7)
• If you have to change the cable & sensor
• If the readings of your ThemoProbe, checked against a calibrated thermometer, are not within +/- 0.5 °F

If your ThermoProbe indicates “-1” or “1” or “E-1”, this is indicative of an open circuit in the sensor circuit, and normally means that replacement of the cable and sensor is necessary.

Changing the Sensor & Cable

Physical replacement of the cable and sensor is easily accomplished with normal tools – but take care with the connection of the cable to the main board. It is extremely important that the black (or ground) cable wire is connected to the ground cable connection (on the model TP-2 this is the terminal closest to the face of the instrument) and that the white wire is connected to the other terminal. IF POLARITY IS REVERSED THE THERMOPROBE WILL NOT FUNCTION.

Calibration Procedure

1. Prepare the following equipment

• A bath for 32 °F or 0 °C (a Thermos bottle with crushed ice works just fine)
• A constant temperature bath for a high temperature (preferable 195 °F or 90 °C). The actual temperature of the bath is not important, but the temperature must be stabile and should be measured by a calibrated thermometer.
• A third bath, to check mid-scale, approximately 110 °F or approximately 43 °C. Again, the actual temperature of the bath is not important, but the temperature must be stabile and should be measured by a calibrated thermometer.

2. Prepare the ThermoProbe for calibration – carefully inspect the cable and sensor for indications of physical damage (cuts, cracks in the insulation, etc)

Model TP-2
Open the case by removing the four screws, and look for and locate three (3) potentiometers – one is labeled “zero”, another “span” and the third is labeled “high span”. We are not going to adjust the “high span”.

Model TP-5
Remove the two black screws on the front of the case. Inside are two potentiometers; the lower one is the “zero” and the upper one is the “span”

Model TP-3 and TP-7
Remove the three screws on the face and carefully remove the faceplate. Locate the “zero” and “span” potentiometers.

Model TP-8
On the base of the instrument is a rubber bushing which seals access to the calibration potentiometers. Carefully remove it and locate the “zero” and “span” potentiometers.

Place the sensor in the 32 °F (0 °C) bath and allow it to come to equilibrium (3 minutes is usually sufficient). Adjust the “zero” potentiometer so that the unit reads exactly 32.0 °F (or 0.0 °C) Place the sensor in the high temperature bath, wait 3 minutes, and adjust the “span” potentiometer so that the unit indicates the temperature of the bath (+/- 0.1 °F or 0.1 °C) You will in all likelihood need to repeat this process 2 or 3 times until the unit reads correctly at both the high and low temperatures. When it reads correctly at both temperatures, check it in the middle bath – it must read correctly in the middle bath with precision of +/- 0.3 °F (+/- 0.2 °C) If it does not read well in the middle bath, check the low and high calibrations again. If you cannot adjust it to read well in the middle you probably need to replace the cable and sensor.

If you have problems, call us and with pleasure we’ll help you with the procedure!

The American Petroleum Institute’s (API) publication ‘Manual of Petroleum Measurement Standards’ (Chapter 7, Section 3) ‘Static Temperature Determination Using Portable Electronic Thermometers’ (First Edition, July 1985) offers specific recommendations for recalibration and verification of your electronic digital thermometer. The following section, has been reprinted, with permission, courtesy of the American Petroleum Institute, as a customer service.

The newest version of Chapter 7, dated June 2001 has the same requirements.

To purchase this or other API standards, please contact the American Petroleum Institute’s Publications Department at 202-682-8000

7.8.2 Initial Calibration

Before initial use, and at least once a year thereafter, each portable electronic thermometer shall be re-standardized in a laboratory or other qualified calibration facility. The thermometer shall be re-standardized by comparing it at three or more temperatures with either a National Bureau of Standards (NBS) (ICL note: NBS is now NIST) certified thermometer or an equivalent thermometer with accuracy traceable to the NBS in accordance with the manufacturer’s instructions. These standardization checks will ensure that accuracy is maintained within the limits given in Table 3.

8.2.1 Field verification

Before each use, or once per day (whichever is less frequent), portable electronic thermometers should be spot checked by comparing the ambient reading against an ASTM glass stem thermometer in liquid. If the readings differ by more than 0.5 degree F (or 0.25 degree C), the portable electronic thermometer should be re-standardized before it is used for custody transfer.

8.2.2 Monthly Verification and Inspection

On a monthly schedule, the portable electronic thermometer should be checked at two or more temperatures near the ends of its range against an NIST certified thermometer or an equivalent thermometer with accuracy traceable to the NIST. Make this check by placing the two thermometers side-by-side in a circulating bath and leaving them undisturbed for at least 10 minutes before making comparative readings. Alternately, the ice point and boiling point of fresh water may be used for accuracy check. The boiling point of fresh water must be corrected for altitude. If the thermometer readings differ by more than the tolerances listed in Table 1, the thermometer should be re-standardized (see 7.8.2)

In addition, the following physical checks should be made:

1. The junction between the cable and the probe should be checked for mechanical damage.
2. The cable insulation should be checked for cuts, breaks, or abrasion.

TABLE 3 – Portable Electronic Gauging Thermometers

Reproduced with permission from API

ICL Calibration Laboratories can perform this calibration and certification for you with a one to two day turnaround.