229 探头可测量土壤水势，测量范围 -10至-2500 kPa。需与CE4或CE8电流激发模块共同使用。Campbell Scientific 的数据采集器控制电流激发模块，测量和计算土壤水势。
|Operating Temperature Range||-5° to +30°C|
|Normal Environmental Temperature Range||-40° to +70°C|
|Measurement Range||-10 to -2500 kPa|
|Measurement Time||30 s (typical)|
|Thermocouple Type||Copper/constantan (type T)|
|Heater Resistance||~34 Ω|
|Resolution||~1 kPa (at matric potentials < -100 kPa)|
|Diameter||1.5 cm (0.6 in.)|
|Length||6.0 cm (2.4 in.)|
|Cable Weight||~23 g/m (0.25 oz/ft)|
|Sensor Weight||10 g (0.35 oz)|
Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.
Either a CE4 or CE8 current excitation module is required to provide a constant current to the heating element of the 229. The CE4 and CE8 differ only in the number of 229 sensors to which they source current. The CE4 sources current for up to four 229s, and the CE8 sources current for up to eight. Both modules require a 12 Vdc power source.
In applications that require more sensors, the output(s) of the CE4 or CE8 can be connected to as many AM16/32-series multiplexers as there are outputs, greatly expanding system capacity. If using multiplexers, the user should be aware that switching currents of greater than 30 mA will degrade the contact surfaces of the mechanical relays. Therefore the data logger should be programmed to turn off the current excitation module before switching multiplexer channels in order to protect the multiplexer relays.
One differential channel and one current excitation channel per probe are required. Each CE4 or CE8 current excitation module requires one data logger control port.
The 229 is measured by a sequence of data logger instructions where the thermocouple is measured at 0 s, 1 s, and 30 s, while a 50 mA current is applied to the heating element. This current is supplied by the CE4 or CE8 current excitation module. The rise in temperature during heating is related to the soil water matric potential.
A reference temperature measurement is required. Options for measuring the reference temperature include:
Very low values for dT, especially negative values, indicate that the 229-L sensor is not heating during the measurement time. The most likely causes are damage to the heater wires, one or more loose wires, or a failure of the constant current excitation module.
The first check to make is of the heater wire itself. With an ohmmeter, measure the resistance between the black and green wires on the 229-L. The resistance should read approximately 33 to 36 ohm. An off-scale or infinite reading indicates a break in the heater wire. A low reading could indicate a short in the heater wire. In both of those cases, the fix would be to dig up the sensor wire and examine it for damage.
The next check is to make sure that there are good electrical connections in the following locations:
Each of those wires should have approximately a quarter inch of bare copper securely connected to its terminal.
Finally, the CE4 or CE8 constant-current module can be checked with a multimeter to make sure it is putting out 50 mA. Measure the voltage between the 12V and ground terminal screws to make sure that the constant current module is receiving power from the data logger. Next, temporarily move the wire connecting the data logger control port with the CTRL channel to a 5 V channel on the data logger to force the module to be on all the time, so that the current output can be measured. Set the multimeter to measure milliamps, and measure the current. It should be 50 mA ± 1 mA. If the current output is outside that range, the constant current module needs to be repaired or replaced.
Yes. Campbell Scientific recommends measuring and recording the temperature of the sensor before turning on the heater. That reading can be used as a soil temperature reading. As long as matric potential measurements are not made more frequently than once every 15 minutes, there will be no significant heat buildup in the sensor, and the sensor temperature will be the same as the soil temperature.
The heater wire itself should read around 33 ohm for resistance, but the green and black wires connected to the heater wire will also add resistance to the reading. The longer the sensor cable, the greater the resistance reading will be. Therefore, readings of 37 to 48 ohm are within the normal range. A resistance reading of infinity or of less than 33 ohm would be caused by a break or short in the sensor cable and would be cause for concern.
At this time, Campbell Scientific does not offer a calibration service for the 229-L. There are companies that offer this service. Contact Campbell Scientific for details.
If all the errors were summed in a worst case scenario, the thermocouple accuracy would be ±0.5°C. For an extended discussion about thermocouple measurements, refer to the "Thermocouple Measurements" section in the data logger manual.
The heating element is made of Evanohm wire. The element is encased in epoxy inside a stainless-steel hypodermic needle and is not exposed to the corrosive environment. Therefore, that part of the sensor should not fail in five years. However, the sensor cable and the ceramic matrix might suffer damage after being exposed to a corrosive environment for five years.
不是每一种传感器都有不同的线缆尾端选项。通过查找传感器产品页面的订购栏 (Ordering tab) 中的两个位置，可以检查某种特定传感器的可用的线缆尾端选项：
如果传感器以 –ET, –ETM, –LC, –LQ, 或 –QD 等版本的型号供应，那么线缆尾端选项已经反映在该传感器的产品型号中。例如，034B 以 034B-ET, 034B-ETM, 034B-LC, 034B-LQ, 和 034B-QD 等型号供应。
所有其它的线缆尾端选项，如果可用，会列在该传感器产品页面的订购栏 (Ordering tab) 中的线缆尾端选项 (“Cable Termination Options) 区域。例如，034B-L 风速风向传感器具有 –CWS, –PT, 和 –PW 等线缆尾端选项，显示在 034B-L 产品页面的 订购栏 (Ordering tab) 位置。
注： 当更新的产品添加到我们的库存中时，一般来说，我们会在单个传感器的产品型号下面列出多种线缆尾端选项，而不是创建多个产品型号。例如，HC2S3-L 具有 –C 线缆尾端选项用于连接到 CS110，而我们并没有使用 HC2S3-LC 产品型号。
大多数 Campbell Scientific 传感器的型号中都带有 –L，它表示用户指定线缆长度。如果传感器型号名称列有 –LX (这里 “X” 是其它的某个字符), 那么该传感器需要用户指定长度，但线缆尾端会配有用于某个独特系统的特殊快速接头：
如果一个传感器的主型号数字的后面没有被指定 –L 或其它的 –LX 字符，那么该传感器将具有固定的线缆长度。在产品页面订购栏中 (Ordering tab) 的描述字段的末尾，会列出线缆的长度。例如 034B-ET 型号的描述字段含有信息：Met One风传感器适用于ET气象站，67英寸线缆 (Met One Wind Set for ET Station, 67 inch Cable)。产品按固定的线缆长度做尾端处理，默认是尾线方式。
如果线缆尾端配有用于某个独特系统的特殊快速接头，则型号尾部的字符会指定该传感器用于哪一个系统。例如，034B-ET 型号表明该传感器是一个 034B 且用于 ET107 系统。
Campbell Scientific 的很多传感器都有可行的不同线缆尾端处理选项，包括以下几种：
注： 线缆尾端选项的可行性因传感器而异。例如，传感器可能会有 无选项、两个选项或几个选项可供选择。如果预期的选项没有列在所指定的传感器中，请联系 Campbell Scientific 的应用工程师寻求帮助。