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Rotronic® HygroClip 2™ Temperature and RH Transmitter Calibration Exchange Program

HygroClip-2 Basics

The Rotronic HygroClip-2 is a digital, temperature and RH transmitter. This transmitter consists of a microprocessor and an ASIC circuit, both of which are located in the probe, along with the capacitive RH sensor and the RTD temperature sensor.

The calibration constants, for both temperature and RH, are stored in the probe itself. The Parameter controller communicates with the HygroClip-2 using a digital format. The Parameter controller does not have the capability to alter the HygroClip-2 data. This means that since the calibration constants are stored in the probe, and since the data is in a digital format, the calibration does not have to be performed on-site. This usually results in a substantial savings in calibration costs.

The HygroClip-2 is shipped from the manufacturer (Rotronic Instruments) with a factory default calibration. This calibration involves offset constants for temperature and relative humidity. These constants are programmed into the device and cannot be erased. That allows the customer to revert back to the factory default calibration at any time (with the assistance of Rotronic HW4 interface software and the proper cables).

The after market calibration, either provided by Parameter, the customer, or a third party calibration provider, will enter additional offsets into the transmitter. These offsets will work with the factory default constants to skew the factory provided calibration curve. This will allow the output to be corrected for any errors that may occur over time.

  • The temperature curve can only be adjusted at a maximum of two points (typically referred to as zero and span).
    • If the temperature is adjusted at only one point (zero) the factory default calibration curve will be offset for an equal amount over the entire range of the sensor. This is known as a single point temperature calibration and the adjustment is called an offset adjustment. This calibration is only traceable at the point of adjustment. Any deviation in measurement from that point includes some level of uncertainty. For this reason, Parameter can perform, but does not recommend, a single point calibration.
    • If the temperature is adjusted at two points (zero and span), the factory default calibration curve will be adjusted in two ways; offset and gain.
      • The offset adjustment will again adjust the entire curve up or down. This adjustment should be performed near the lower end of the operating range of the device.
      • The gain adjustment will adjust the slope of the calibration curve. This adjustment should be performed near the upper end of the operating range of the device.
  • The RH curve can be adjusted at a maximum of 100 points. The more adjustments that are made, the more accurately the curve will represent the actual RH being measured.
    • If the RH is adjusted at a single point (zero) the factory default calibration curve will be offset for an equal amount over the entire range of the sensor. This is known as a single point RH calibration and the adjustment is called an offset adjustment. This calibration is only traceable at the point of adjustment. Any deviation in measurement from that point includes some level of uncertainty. For this reason, Parameter can perform, but does not recommend a single point calibration.
    • If the RH is adjusted at two points (zero and span), the factory default calibration curve will be adjusted in two ways; offset and gain.
      • The offset adjustment will again adjust the entire curve up or down. This adjustment should be performed at a value less than the anticipated operating range of the device.
      • The gain adjustment will adjust the slope of the calibration curve. This adjustment should be performed at a value greater than the anticipated operating range of the device.
      • This adjustment scheme will provide some level of certainty that the device is within tolerance at all values that fall between the two adjustment points.
    • It can also be desirable to adjust the RH at more than two points.
      • The two most extreme (high and low) points will provide the same offset and gain adjustments described above.
      • Any additional points will act to “curve fit” the factory default calibration. This will provide additional accuracy over the range of the device. The more points that are adjusted the more accurate the measurement will be.
    • Regardless of the number of RH points that are adjusted, or the temperature at which these adjustments are made, all RH offsets are referenced to a temperature of 23°C. That means that even if the RH is adjusted at 40°C @ 75% Rh, the offset that is stored in the transmitter is internally calculated for a 23°C temperature. For this reason, Parameter recommends that all RH calibration points should be adjusted at 23°C. If additional verification is required at a different temperature, this can be done, but an additional charge will apply.

Standard Calibration

This calibration is targeted toward chambers with a maximum operating temperature of 60°C or less.

  • The HygroClip-2 sensor temperature will be calibrated at 20°C and 45°C
  • The HygroClip-2 sensor RH will be calibrated at 35% and 80% RH at a temperature of 23°C.

Options:
The following modifications and/or additions can be added to the standard calibration at no additional charge:

  • The minimum and/or maximum temperature at which the sensor is adjusted can be modified.
  • The minimum and/or maximum RH at which the sensor is adjusted can be modified.
  • The temperature at which the RH is calibrated can be modified.

The following modifications and/or additions can be added to the standard calibrations. An additional charge will apply:

  • Additional temperature points can be verified. Verification does not include any adjustment. The sensor will be operated at the additional points and the measured value will be compared to the temperature reference standard. The as-found and reference values will be documented on the calibration certificate.
  • Additional RH points can be adjusted. This will include an as-found and as-left value since the RH can be adjusted at up to 100 points. The as-found, as-left and reference values will be documented on the calibration certificate.

Calibration Sensor Options

There are several calibration options for the HygroClip-2, including on-site calibration, reserve sensors and an exchange program.

1.) Reserve Sensors:
A reserve sensor means that the customer will purchase an identical HygroClip-2 transmitter, calibrated to their requirements. The two sensors (control sensor and reserve sensor) will be interchanged in order to maintain a calibrated sensor in the system at all times. The sensor that is not in the system will be sent off-site for calibration, as required.

  • The main advantage to this system is that there will always be a spare sensor in case of sensor failure.
  • The main disadvantage to this system is that the calibration costs will be exactly double if both sensors are have valid calibrations at all times.

Parameter has a variety of sensors available – please call for pricing.

2.) Exchange Program:
The Exchange program will allow the customer to receive a reconditioned, calibrated HygroClip-2 transmitter, immediately before the transmitter in their system is due for recalibration. The replacement transmitter is installed in the system and the transmitter in their system is then returned to Parameter as trade-in. Parameter has a variety of sensors available – please call for pricing.

Documentation

All Parameter calibrations are performed using NIST traceable temperature and chilled mirror dew point sensors.

All Parameter calibrations will include “as-found” and “as-left” data. For the exchange program, the “as-left” data will be referenced to the exchanged sensor, and the “as-found” data will be referenced to the trade-in sensor. In the exchange program, the calibration certificate will be mailed after the trade-in sensor has been evaluated for the “as-found” data.