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* 1-Wire® Components by Betatronics *
* These sensors use Dallas Semiconductor Products *
* "1-Wire®" is the registered trademark of Dallas/Maxim *
" Betatronics is a manufacturer (vendor) of packaged sensors "

Common Sensor (probe) Details:

Most Betatronics sensors using Dallas 1-wire components operate in a three wire bus mode.
     However, there is no problem using the temperature sensors based on the DS-18B20 in a
     two wire mode by simply connecting the +V power supply line to common.

Temperature sensors -- use the Dallas 1-wire temperature sensor DS-18B20.
     Temperature resolution is 0.0625 C (0.11 F), i.e. 1/16 C.
     The Dallas part alone functions from -55 C to +125 C (-67 F to +257 F).
     Dallas specifies accuracy of
          +/-0.5 C from -10 C to +85 C (14 F to +185 F), and.
          +/-2 C from -55 C to +125 C (-67 F to +257 F).
     With individual calibration short time accuracy can approach resolution.
     Three wire mode allows simultaneous measurement by all connected sensors, and
          allows other control or data bus traffic during temperature measurement.
          Simultaneous temperature measurement shortens total loop time per measurement.
          Sensors using other components with the Dallas chips can derive power from
          the power wire in the three wire mode.
     Using the 3 wire bus mode many sensors can have their measurements initiated
          simultaneously, and read out faster than once every 2 seconds.
     Dallas temperature measurement time is approximately 750 milliseconds (0.75 seconds).
     Minimum repetitive cycle time is determined by the number of sensors and baud rate.

Standard cable is vinyl telephone wire with a maximum specification of 60 C (140 F), and
     is 4 conductor, #26 AGW, stranded, flat. This cable is not for continuous flexing
     applications. Use a separate sacrificial cable in the area where continuous flexing occurs.
High temperature cable with or without a connector is available on special order at extra cost.

All RJ14 connectors use a standard Betatronics pinout. See definition below at:
     The Betatronics cable and pinout philosophy.

Use regulated 5 V DC +/-5% to power the sensors. For example -- ua7805C.
     However, a voltage variation from 3 to 6 V appears to produce less than 1/16 C
          variation in measured temperature, i.e., less than the sensor resolution.
     During temperature measurement the active current of the Dallas 1-wire sensor
          DS18B20 is about 1.5 mA while standby current is in the range of 0.001 mA.
Maximum cable length for a 1-wire network is a function of your noise envirnoment, cable
     capacitance, cable layout, and number of sensors.

Ordering Information:

Phone 734-930-6136      USA eastern time zone


USA sales only.

BTW1-11 . . . . . . . . . . . . . . . $ 20
Temperature sensor, or probe.
Closed end round brass tube, epoxy filled, 0.343" x 1.20".
     Should mount in a 11/32" reamed hole. Use antiseize
     grease. Only clamp circumferentially.
Temperature range -55 C (-67 F) to 60 C (140 F),
     maximum temperature is cable rating limited.
Thermal time constant (63 % change) ---
     Approx   20 seconds fully inserted in a 0.343" dia,
          hole in an aluminum heatsink.
     Approx 200 seconds vertical in still air.
Integral cable is about 12 ft long terminated in an RJ14 plug.
Only the sensor tip can be liquid immersed.
     Do not fully immerse in liquid.
Suitable for outdoor use with cable down.
At extra cost high temperature cable with no plug can be supplied.
     Appropriate connectors can be provided. Special
     modifications can be made. This basic sensor can be
     designed into an NPT pipe fitting.
3 oz, weight.

BTW1-11-25 . . . . . . . . . . . . . $ 27
Temperature sensor, or probe.
Same as BTW1-11 except ---
    25 ft cable.
    Should allow plug to be indoors for outside measurement.
    For maximum cable life protect the cable from sunlight, water, and outside elements.
6 oz, weight.

BTW1-14 . . . . . . . . . . . . . . . $ 25
Temperature sensor.
1.05" x 1.45" flat aluminum base. 1.0" high.
Two #28 (0.141") mounting holes, 0.75" center to center.
     Use 6-32 x 1.25" machine screws.
Temperature range -55 C (-67 F) to 70 C (158 F),
     maximum temperature is limited by the AMP connector
     rating. Cable used could be a further limit.
Thermal time constant (63 % change) ---
     Approx   40 seconds in contact with aluminum heatsink.
     Approx 700 seconds vertical in still air.
No cable. Standard Betatronics pinout on RJ14 connector.
For machine mounting, or to an adapter to pipe. For shortest
     thermal constant mount on a machined flat surface.
Not for liquid immersion.
Not for outdoor use.
2 oz, weight.

BTW1-17 . . . . . . . . . . . . . . . $ 38
Temperature sensor or probe, plenum or liquid probe.
     Liquid immersion only on sensor closed end of tube.
Closed end round 316 stainless tube, epoxy filled only in
     the sensor region. Because of the thin wall to reduce
     thermal conductivity the tube can be crushed easily.
     Clamp only by the full circumference.
     0.375" x 12" x 0.028"
Temperature range ---
     -55 C (-67 F) to 125 C (257 F), at sensor end.
     -55 C (-67 F) to   70 C (158 F), at connector end.
          Maximum is limited by the AMP connector rating.
          Cable used could be a further limit. Heatsink
          mounting of the tube may be necessary to limit
          the connector end temperature.
Thermal time constant (63 % change) ---
     20 seconds, about, in an aluminum heatsink.
     600 seconds, about, vertical in still air.
No cable. Standard Betatronics pinout on RJ14 connector.
Not for outdoor use.
10 oz, weight.

BTW1-22 . . . . . . . . . . . . . . . $ 22
Temperature sensor. Faster response in forced air,
     or radiant applications.
PC board 1.1" x 2.0", 0.75" high.
Two #32 (0.116") mounting holes, 0.875" center to center.
     Use 4-40 machine screws.
Dallas chip open on PC board with connector. Delicate.
Temperature range ---
     -55 C (-67 F) to 70 C (158 F), max is limited by the AMP
     connector rating. Cable used could be a further limit.
Thermal time constant (63 % change) ---
      6 seconds, about, high velocity air.
     200 seconds, about, vertical in still air.
          Very approximate, hard to define and measure.
No cable. Standard Betatronics pinout on RJ14 connector.
Not for outdoor use.
Not for liquid immersion.
0.3 oz, weight.

The Betatronics cable and pinout philosophy.

The Betatronics pinout for Dallas 1-wire bus (network) devices is different than the Dallas pinout. Betatronics uses a three wire mode with a four wire cable, and a six position connector with the center four pins populated (RJ14).

First, we think there is very little value in operating "1-wire" bus devices in the two wire mode for the sensors we are providing. The three wire mode provides more general utility. However, a three wire mode sensor can have its +5 V pin connected to common and then used in the two wire mode. In two wire mode data communication can not take place while a 1-wire device requires power. In particular the Dallas temperature measurement chip, DS18B20, requires about 1.5 mA at a stable voltage (normally +5 V) while doing a measurement and this lasts about 0.75 seconds.

Second, since only three wires are required the standard telephone RJ14 type connector with only the middle four contact positions populated has been selected. Four wire premade cords are easy to find, and the readily available five position paralleling blocks are useable. These blocks are typically only populated in the middle four positions.

Third, having made these decisions the ordering and positioning of the wires are based on ease of cable assembly, or connection to the Dallas DS18B20 chip.

The Betatronics pinout is:

     Pin 2 Yellow --- Vdd +5 V.
     Pin 3 Green --- Data in and out.
     Pin 4 Red --- Common (may be called ground, but should not be grounded at sensor).
          If grounded, then this should be done at only one point, and that one point
          should be at the command point of the network.
     Pin 5 Black --- Another possible Common and may be connected to common (pin 4) in
          some sensors.

The Dallas pinout is:

     Pin 1 Vdd +5 V.
     Pin 2 Common.
     Pin 3 Data in and out.
     Pin 4 Another common, but from the DS9503.
     Pin 5 Dallas SUSO.
     Pin 6 No connection.

To correctly map the two pinouts to each other our patch cord from Dallas to Betatronics maps pin 3 to 3, and 4 to 4, and Dallas pin 1 to Betatronics pin 2. Once the conversion is done in one location, then all cables must be straight thru.

A caution on cables and wiring. Never connect the wrong voltage and polarity to any sensor pin. Thus, you must check that cables are wired correctly. Some commerical phone cables might not be wired as straight thru cables. Also some couplers might not be straight thru. What does straight thru mean? It means pin 1 to pin 1, pin 2 to pin 2, etc.

Temperature ratings.

All materials have characteristics that vary with temperature. Most materials will soften with increasing temperature, and get stiffer as temperature is reduced. Some materials are composites or mixtures of several components. Each with different characteristics. Temperature ratings of products are determined by how the various components change with temperature. All our sensors are made of different components. The component with the lowest or more limited rating will determine the overall sensor rating.

All our temperature sensors use the Dallas 1-wire DS 18B20 sensor. This device has a maximum rating range of -55 C to +125 C (-67 F to +257 F). This means the materials in the sensor can tolerate this range over a reasonable lifetime. Also it means data can be obtained over this range.

The epoxy used for encapsulation has a service temperature rating of -55 C to +155 C (-67 F to 311 F). Somewhat greater than the Dallas chip.

Both brass and 416 stainless steel are useful in our applications, and have even greater useful temperature ranges.

The normal plastic, plastic wire, and connectors we use have more limited temperature capability. PVC cable is the lowest rating, 60 C (140 F). AMP connectors at 70 C (158 F). Delrin (acetal resin) as we apply it is probably useful to 80 C (176 F). FR-4 glass epoxy PC stock is rated to 140 C (284 F). On special order high temperature cable can be supplied.

You should note that PVC cable uses a plastizer to soften the PVC. Hydraulic oil, other chemicals, or the environment may leach the plastizier from the cable making it stiff, thus cracking with flexure, and resulting cable failure.

Depending upon the material, if you use it outside of its rated range, then the lifetime of the sensor may be greatly degraded.

We have performed some limited severe thermal shocks to our sensors from a 120 C (248 F) aluminum heat sink to contact with dry ice -78.5 C (-109.3 F). The Dallas chip was monitored and cycling occurred when the temperature as measured by the Dallas chip reached -50 C (-58 F) and 100 C (212 F).

How the Dallas 1-Wire Temperature Sensor System Works.

The Dallas 1-Wire sensor system can be described as a parallel bus command response network system.

What does this mean? A parallel bus of 2 or 3 wires is strung out over some space with various addressable sensors distributed over that space and connected in parallel across the bus. Also connected to the bus is a master device that sends commands to the sensors, and from most commands expects a response from the addressed sensor. The sensors and master can be connected anywhere on the bus. The bus can be one long cable or many shorter ones in parallel. The network topology may limit the maximum total cable length. The bus must consist of a reference line (common)(return), a +5 V power line (in some applications somewhat lower voltage can be used), and a data line. The data and power lines are referenced to the common line. The reference line is likely called ground, and may or may not be grounded (earthed). Our preferred name is common.

Each sensor has a unique address so that the master can communicate with a single sensor and receive a response from that sensor without interference from other sensors. The master can also broadcast a message to all sensors at once, but for this type of message there can not be a response from any sensor.

If the system is operated in the 2 wire bus mode, then the data line is also the power supply line. These two functions, power and data, have to be time shared. Both functions can not exist at the same time. This means the master or a sensor can not transfer data while one or more other sensors require power. For a temperature sensor power is required for about 0.75 seconds. During this time the data line has to be a fairly stiff stable voltage source to all sensors requiring power. Whereas, to transfer data the data line has to be supplied by a fairly small current source in place of the stiff voltage source. A stiff voltage source means very little voltage variation with changing load current up to some maximum value.

In the 3 wire bus mode a third wire is added for the sole purpose of supplying a stiff voltage source to all devices on the bus all the time. Now the data line only serves the purpose of transferring data. Data can transfer at any time. But data transfer can only occur from one device at a time. This includes the master. In other words the system must operate in a half-duplex mode. The data flows bi-directionally, but at any time in only one direction.

Device addresses look like the following string of hexadecimal numbers:
28 B4 B4 FF 02 00 00 31
The least significant 8 bits are a family code, 28h is family code for the DS 18B20. The next 48 bits are a unique serial number, and the most significant 8 bits are a CRC error check code of the preceeding 56 bits. The entire 64 bits can be viewed as the address. A temperature sensor always starts with a 28. The last number (shown here as 31) is a CRC check code of the message (the least significant 56 bits)(family code plus the serial number). The unique address has 256 exp 6 combinations, or 2 exp 48. Which is 280,000,000,000,000 possiblities. The time order of transferring data over the bus is as in the above sequence from left to right.

A sensor and bus system of this type has the potential advantage of simplifying wiring and providing one or more means of detecting certain system failures. If a master sends a command to a sensor and there is no response, then a system or sensor failure has occurred. If only certain sensors fail to respond, then those sensors, or the communication path relating to them has failed. The response time to detect such a failure is the scan time to all the sensors.

Where you have sensors that should have a changing output with time, and there is knowledge of how this variation and its amplitude are expected to occur with time, then comparing this a priori knowledge with the present data provides a further system check.

Outdoor temperature measurement illustration.

The photo at the right shows the BTW1-11-25 in an outdoor application. The sensor is mounted with its closed end up. The mounting rod is wood and the sensor is spaced slightly above the rod top end. This minimizes thermal conductivity from the rod and ground.

Mounting is about 4' above the ground, 3' from the wall, and on the north side with shading from the sun most of the day. The vinyl cable can only self support the sensor a short distance above the mounting rod.

A several inch diameter open ended tube, a tin can, can be coaxially placed around the sensor to protect from radiant energy striking the temperature sensor, for example direct sun light.

Six foot wood handles can be found in hardware stores.

This mounting arrangement shown is simple and seems to have weathered well. It has been untouched for about two years. Scotch 33 tape was used to attach the cable to the rod.

Example plot of time correlated outside and inside temperatures.

Outside sensor is a BTW1-11-25 as shown in the previous photo. Inside sensor is a BTW1-22 adjacent to the thermostat controlling the furnace. This is a real application of the Dallas DS-18B20 chip.

This plot is a 24 hour period for one day.
Sampling is every 2 seconds, time resolution is 2 seconds, and temperature resolution is 1/16 C, or approximately 0.11 F [ (9/5)*(1/16) ].

Red curve -- Outside temperature varied from 33.2 F to 42.8 F. Min to max is 9.6 F.
Black curve -- Inside temperature varied from 67.4 F to 67.8 F. Min to max is 0.4 F.


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