229-L 水势传感器
测量结果可靠
不需维护
气象 应用支持 水资源 应用支持 能源 应用支持 湍流通量 应用支持 基础结构/工业设施 应用支持 土壤 应用支持

概览

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。

优势与特点

  • Compatible with most Campbell Scientific data loggers
  • Measures a wide range of matric potential
  • Measurements not affected by salts in the soil
  • Long lasting, with no maintenance required
  • Compatible with AM16/32-series multiplexers, allowing measurement of multiple sensors

图像

技术说明

229 水势传感器由加热元件和热电偶组成,热电偶置于装有环氧树脂的内管中,内管用多孔陶瓷包裹。

为计算土壤水势,CE4或CE8电流激发模块向229加热元件发出50mA的电流,热电偶可测量出温度上升。在多孔性陶瓷基体,从而改变为周围的土壤润湿和干燥的水的量根据不同的温度上升的幅度。根据多孔陶瓷基体处的水量,例如土壤潮湿或干燥,温度会有不同的上升幅度。土壤水势根据温度上升的数据利用二阶多项式计算得来。用户在使用229时,务必根据自身土壤情况进行相应的校准。

229的热电偶测量时需要一个参考温度,参考温度传感器内置在大多数数据采集器的接线面板上。

产品规格

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)

兼容性

Please note: The following shows notable compatibility information. It is not a comprehensive list of all compatible products.

数据采集器

Product Compatible Note
21X (retired)
CR10 (retired)
CR1000X
CR10X (retired)
CR200X (retired)
CR206X (retired)
CR211X (retired)
CR216X (retired)
CR23X (retired)
CR295X (retired)
CR300
CR3000
CR310
CR500 (retired)
CR5000 (retired)
CR510 (retired)
CR6
CR800
CR850
CR9000 (retired)

Additional Compatibility Information

Current Excitation Modules

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.

Multiplexers

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.

Data Logger Considerations

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.

Programming

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.

Reference Temperature Measurement

A reference temperature measurement is required. Options for measuring the reference temperature include:

  • Thermistor built into the CR800, CR850, CR1000, CR3000, or CR5000 wiring panel
  • PRT built into the wiring panel of the CR9050 or
  • CR9051E input module for the CR9000X Measurement and Control Datalogger
  • PRT built into the wiring panel of the CR723T input card for the CR7 Measurement and Control Datalogger
  • CR10XTCR thermistor that connects to the CR10X wiring panel

常见问题解答

229-L: 11

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  1. For details and sample programs, see the "Example Programs" section of the 229-L manual.

  2. 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:

    • where the black and green sensor wires connect to the constant current interface or to a multiplexer
    • where the multiplexer common wires connect to the constant current interface
    • where the constant current interface connects to the data logger 12V, G, and control port

    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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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:

    • 产品型号
    • 线缆尾端选项列表

    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。

  9. 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:

    • –LC 表示用户指定线缆长度,所配快速接头用于 ET107, CS110, 或已停产的 Metdata1 系统。
    • –LQ 表示用户指定线缆长度,所配快速接头用于 用于 RAWS-P 气象站。

    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。

    • 以 –ET 结尾的型号的传感器配备快速接头,用于 ET107 气象站。
    • 以 –ETM 结尾的型号的传感器配备快速接头,用于 ET107 气象站,但它们也含有一个特殊的系统安装支架,在订购一个备件时,所配的支架经常是便捷实用的。
    • 以 –QD 结尾的型号的传感器配备快速接头,用于 RAWS-F 快速配置气象站。
    • 以 –PW 结尾的型号的传感器配备快速接头,用于 PWENC 预接线机箱或预接线系统。
  10. 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:

    • –PT (–PT w/Tinned Wires,镀锌尾线) 是默认选项,不显示在产品行中,而其它选项会显示在产品行中。线缆末端为尾线方式,可直接连接到数据采集器。
    • 在 –C (–C w/ET/CS110 Connector,CS110快速接头) 选项中,线缆尾端所配的快速接头可连接到 CS110 电场计或 ET-系列的气象站。
    • 在 –CWS (–CWS 带 CWS900 快速接头) 选项中,线缆尾端所配的快速接头可连接到 CWS-系列的接口。连接到 CWS900-系列接口使得传感器可被用于无线传感器网络中。
    • 在 –PW (–PW 带预接线快速接头) 选项中,线缆尾端所配的快速接头可连接到预接线机箱上。
    • 在 –RQ (–RQ 带RAWS 快速接头) 选项中,线缆尾端所配的快速接头可连接到 RAWS-P 永久配置远程自动气象站。

    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。

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