Can I use thermal adhesive tape for protecting DS18B20 from 440V AC lines ?

Clamping/taping with DS18B20 to high voltage lines will damage the plastic packaging of the DS18B20 and could eventually lead to an electrical short from that 440V to the DS18B20.

Do you have a DS18B20 in a metal enclosure?

No we don't, but you can find it here: https://www.adafruit.com/product/381

What is the possible variation in temperature reading of the DS18B20?

The precision of the DS18B20 in the range of -10℃~85℃ is ±0.5℃, which implies that the maximum temperature difference between two different devices in the same environment is 1℃. From our tests in the lab, the temperature difference between different devices is generally within 0.5℃.

How do I use an oscilloscope to capture the signal of remote 1-Wire equipment?

A differential probe is recommended for reading remote 1-Wire equipment. The reference ground of the probe should be floating, otherwise the ground of probe will bypass the reference ground of 1-wire, thus leading to a change of topology. If the differential probe is not available, it must be guaranteed that the ground of the oscilloscope is isolated from the ground of the bus, or the oscilloscope with battery as the power supply should be used. Under normal circumstances, the probe of the oscilloscope will not affect data reading. If the probe in your system has caused reading failure, it means the driving capability for remote equipment is close to the limit.

What are the factory default values of TH and TL (upper and lower alarm trigger registers) of the DS18B20?

When sent directly from the factory, TH is 0x4B and TL is 0x46.

Is the DS18B20 radiation hardened?

Unfortunately not. The DS18B20 is not a radiation hardened product.

Does the distance between the DS18B20 sensor to the bus master have an impact on the response time of the conversion?

The distance of the sensor from the bus master has no impact on the response time of the DS18B20 conversion. The DQ line (ie,1-Wire bus) is only transmitting the conversion result that occurred on-board the DS18B20 IC. It is more likely that there is some difference in the insulation/waterproofing of that particular sensor that is allowing thermal conductivity to the DS18B20 through either the package or the GND pin. Keep in mind that the GND pin of the TO-92 package is directly connected to the die of the DS18B20, so if there is close or direct contact of the GND pin to the temperature being measured, then you can expect much better response time. Sensing through the package of the DS18B20 is of course possible, but thermal conduction is much much better through the metal connection of the GND pin to the die inside the package.

Can the DS18B20 and the DS2438 be on the same one-wire bus?

Q. Can the DS18B20 and the DS2438 be used on the same one-wire bus? The DS2438 requires a bus reset to start conversion. Does that mean in parasite mode, we can not allow them to be mixed on the same bus? Or can we wait after bus reset then enable active pull-up? A. You can have both DS18B20 and DS2438 configured in parasite powered mode on the same bus. They both use the Convert T [44h] command, and require the strong pull-up during that conversion when in parasite powered mode. So since both devices use the same Convert T command to initiate a conversion, you will send the Convert T [44h] command (which will start conversions on both parts at the same time), and within 10us engage the strong pull-up for the duration of the conversions. When the conversions are complete, the strong pull-up (MOSFET) can be disengaged, and then you can send separate read commands to get the temperature results from each device.

Do strong magnetic fields affect the performance of the DS18B20?

Maxim has not tested the performance of the DS18B20 when exposed to high magnetic fields. It is not anticipated that the magnetic field would adversely affect measurements, but Maxim does not have any data to support this claim. As with any critical design metric, Maxim recommends testing circuitry as deemed necessary.

Is there a way to send the same command to multiple 1-wire devices simultaneously?

Yes, the skip ROM command allows the master to address all the devices on the bus simultaneously without sending any ROM code information. Skip ROM will allow the next 1-wire command to be sent to all devices, so make sure that only devices of the same family code are present on the bus when doing this. For more information, please reference the "Skip ROM" section in the device data sheet.

Is there a recommended adhesive to use when sealing a housing used to protect the DS18B20?

Maxim does not have a specific recommendation for an adhesive to use. In general, any typical two-component, non-conductive adhesives should work. The adhesive should be a good thermal conductor for best results.

Is there a way to check for power failure by reading registers of the DS18B20?

The DS18B20 does not store any voltage data and cannot be used to track what the supply voltage is. Command [B4h] (Read Power Supply) is only used to determine if the DS18B20 is implementing parasite power mode. The only way to check for power failure is to check the power-on-reset (POR) values of the temperature register. The temperature register will report 85°C after POR and will maintain this reading until a conversion is completed. If there was a brown-out or limited power supplied to the DS18B20, then the temperature register would contain "garbage" data from the ADC result due to the power starved ADC attempting a conversion. Note that this is not a foolproof method but is highly likely to work in most cases.

Is there a condition where parasitic power for the DS18B20 is not recommended?

Yes, parasitic power is not recommended when measuring temperatures above 100°C. At temperatures above 100°C, the DS18B20 may not be able to sustain communication due to the higher leakage currents that can exist at these temperatures. For more powering information, please read "Powering the DS18B20" on page 7 of the DS18B20 data sheet.

Has the DS18B20 been tested against IEC 60751, ASTM E644-98, or ASTM E1137-97?

The DS18B20 has not been tested against these standards because these standards are relevant to RTDs. The DS18B20 is a silicon band gap temperature sensor and thus was not tested against these standards.

Is there any alternative to identifying a DS18B20 other than using its ROM ID?

The DS18B20 has the ability to compare the latest temperature conversion result to the user programmable TH and TL levels (bytes 2 and 3 in the Scratchpad). If the comparator function is not being used, use the TH and TL bytes to set a unique value for a specific DS18B20 device. This requires programming these registers before placing the DS18B20 in the system, but it does allow the user to enter their own 16 bit "identifier" for each DS18B20. The TH and TL limits are stored in EEPROM, so they won't disappear if power is cycled to the DS18B20. If a random DS18B20 is implemented in the system, and the TH/TL registers have been pre-programmed to an identifying value, the user can read the Scratchpad, look at bytes 2 and 3, and determine which device is being used.

Does the C4 revision of the DS18B20 need trim calibration as described in AN247?

AN247 (DS18X20 EEPROM Corruption Issue) only applied to revision B7 of the DS18B20 die. The EEPROM Corruption issue is NOT present in the C4 revision of the DS18B20. Do not perform the trim recalibration described in AN247 on the C4 material. The corruption issue was corrected in revision C4 material, and the AN247 recalibration should not be used with C4 material.

Can the DS18B20 be submerged in water?

The DS18B20 does not have a sealed package and cannot be submerged in water. If you need to submerge the DS18B20 in a liquid, several third parties manufacture sealed temperature probes that use the DS18B20. Maxim does not endorse any particular manufacturer of these probes nor maintain a list of these probe manufacturers.

Do I need to provide the 64 bit address to communicate with the 1-Wire device even if I only have one component on the bus?

If the 1-Wire device is the only device on the 1-Wire bus, then the Skip ROM command can be used instead of the Match ROM command, allowing the user to communicate with the 1-Wire device without using the 64-bit unique ID.

Do the package numbers correlate to the ROM identifier?

The numbers marked on the package represent the date code of assembly, the revision of the silicon, and the internal lot code of the batch. These have no relationship with the ROM identifier. All DS18B20 devices will have a "family" code (first 8 bits of the ROM id) of 28h. But none of the ROM code will be marked on the package of the IC.

Does the +/-0.5°C accuracy include error from the ADC conversion, drift over time, and is it dependent on ADC resolution?

The +/-0.5°C accuracy is guaranteed across the -10°C to +85°C temperature range, and includes error for ADC and any drift over time (which is negligible). Maxim uses two matched transistors with a known voltage differential behavior across temperature. We trim the ADC to generate a digital temperature value corresponding to the known voltage behavior across temperature. So like the curves in Figure 17 of the datasheet, all DS18B20's will have that signature curve. The ADC trim adjusts that curve so that it falls within the +/-0.5°C limits. The resolution determines how many samples of the voltage we take and average, but does not affect the accuracy of that measurement, just the number of bits we report back. The the accuracy is always +/-0.5°C regardless of the resolution.

Other ADI Processors

Documents DS18B20/GG8: FAQ

DS18B20/GG8: FAQ

Partner Forums

Partner Libraries

DS18B20/GG8: FAQ