Remote Control and Supervision of the Relative Humidity Standards of Colombia

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"With LabVIEW a complex, efficient and trustful solution that is attractive and easy to use for the user can be developed in a short time. It also provide the tools for working in almost all (or may be all) areas in engineering."

- Diego Ernesto Ballén Cantor, Universidad Distrital Francisco José de Caldas

The Challenge:
Remote monitoring and control of the national standards of humidity, with the following objectives: 1. Process optimization for calibration of instruments that measure this quantity. 2. Getting remote access to the Colombian standards of humidity from anywhere in the world, via Internet, so that theoretical and practical training (national or international) that are received or issued at this magnitude can make use of this equipment . 3. Minimize the possibility of including measurement errors attributable to the observer in the process of measurement and calibration.

The Solution:
Remotely control the standards (change set point values and start and suspend operation), supervise them and calibrate the devices using a local (near to the standards) and a remote application having them communicated through a TCP connection. Besides develop a PDA application that also communicates with the local one and allows user to control and supervise the primary standards.

Author(s):
Diego Ernesto Ballén Cantor - Universidad Distrital Francisco José de Caldas
Luis Alfredo Chavarro Medina - Humidity Laboratory Manager - SIC, Colombia

Introduction:

The Superintendencia de Industria y Comercio by law preserves and maintains the Colombian national standards of measurement, including the quantity of humidity (see Figure 1). The humidity laboratory has the legal responsibility of disseminating traceability to the units of the International System through calibration of instruments that measure this quantity.
In this field, the National Standard consists of a two pressures Humidity Generator and a Shilled Mirror Hygrometer. The calibration process consists of a comparison of the values given by the humidity generator and that value indicated by the instrument under calibration at certain points of relative humidity. This comparison is made when the entire described system achieves its stability conditions.

The collected data is processed using complex spreadsheet based on Microsoft Excel to determine the errors of the instrument with respect to the standards, as well as uncertainties associated with the measurements. The process culminates with the storage of a spreadsheet of each instrument and the issue of a certificate which is given to the customer with the results of the calibration. All these tasks are currently performed by hand with the additional problem that these equipments are noisy and the temperature in the calibration location tends to increase.

Application Description:

A local application was developed for acquire data from the standards via their RS232 interfaces. It can operate as a server (server mode) by receiving requests from clients (remote application and PDA application) or it can operate as an application that handle the calibration process (calibration mode). When it is executed, it allows the user to choose the operation mode. If a decision is not made, the application after a specific time sets the server mode.

As a server, the local application sets a connection with a client via TCP protocol (see figure 2). Then, data required for the calibration process (such as relative humidity %HR, temperature, pressure, air flow, and others) is send and control commands are wait to be received. Permanently relative humidity from the standards is compared in order to establish when stability conditions are accomplished. Images from a USB camera are also transmitted. It is located inside the generator and allow to see the data coming from the devices (all devices been calibrated are located inside the generator).

This information is received in the remote application which allows sending the data to the spreadsheets. After enter the value of the measure of the device (it is seen in the image received) and press a button, this data is send to the spreadsheet of that device with the value indicated by the generator. All the time the connection status is informed. When all data has been acquired and all calculations have been made, the application generates a calibration certificate (in .pdf format) that is delivered to the client. Also a spreadsheet is saved for each instrument. For access control to this information, each one is created with a specific password. All this description also applies for the local application in the calibration mode.

In order to provide facilities to the user in the supervision, a PDA application has been developed (see figure 3). It allows supervising the standards and controlling operation points (relative humidity, temperature, pressure, and others). Relative humidity from the standards is also compared using a waveform chart which allows establishing when stability conditions are reached, so that data acquisition is feasible. It is also possible to configure network parameters such as IP address of the server and the access port.

Local and remote applications are designed to prevent data losses. The spreadsheets are saved each time a configuration change is made or data is send to the sheets. The control over the standards is entirely up to the application. There are backup files that allow making the calibration process in multiple sessions. This is very useful due to a calibration can last from 1 to 2 days. This way, a later calibration will start exactly the point it was stopped before (all required data will be reloaded). Due to calibration is a sequential process, the application can advance from one stage to another automatically once that stage has been completed. The state of the calibration is informed via pop up windows and specific string fields.
They also inform when to take specific actions in order to prevent run time errors.

Conclusion:

Remote control and supervision of the national primary standards is a project that involves several areas of engineering and has certain complexity. Nevertheless it has been successfully developed using a single tool that offers several advantages over other solutions available in the market.
With LabVIEW a complex, efficient and trustful solution that is attractive and easy to use for the user can be developed in a short time. It also provide the tools for working in almost all (or may be all) areas in engineering.

Author Information:
Diego Ernesto Ballén Cantor
Universidad Distrital Francisco José de Caldas
Colombia
Tel: 573 54 28 - ext. 3402
dballen@correo.sic.gov.co

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