Seca 703 NEC1 Service Manual

Weighing small children to obese patients – the seca 703 can do it all. Especially when it comes to finding out BMI and height. Then there are two options: integrate a mechanical measuring rod or receive data wirelessly from a separate digital stadiometer. Other advantages include the high load bearing capacity of up to 660 lbs for heavyweight patients, the large and flat platform and time-saving functions Pre-TARE, HOLD, Auto-HOLD and mother/child-function. With everything primed for the future and integration in EMR.

Weight measurement Seca 703 NEC1

The DMS modules use load cells with strain gauges in a double bridge circuit as sensors. The entire analog part runs on its own supply voltage. This voltage can be switched by the μC to 3V, 5V or 10V. This voltage is also supplied to the load cells. At full load, they deliver a bridge output voltage of 2mV/V.
This voltage is measured by a dual slope a/d converter. The DMS ext module can evaluate up to four load cells which are multiplexed accordingly. Only one load cell can be connected to the other types of DMS modules. The conversion time is selected so that a new measured value is available every 0.1 s. The resolution of the a/d converter is 0.05 μV/V. If several load cells are connected, keep in mind that the resolution relates to the mean output signal of all the load cells connected. When these measured values are within the expected range, they are converted into a weight value using a third order polynomial. In order to increase accuracy, eight measured values are used to calculate the weight to be displayed. The first value obtained after switch-on is used as the zero point. If the values obtained later on do not deviate strongly from this value, the zero point is corrected in order to compensate for possible drifts. (Please also refer to temperature measurement.)

Seca 703 Calibration Manual

In order to compensate for linear measuring errors of the scale, which can, for instance, occur as a result of the different forces of gravity at different geographical points, the module has a recalibration function. To initiate the function, another button must be pressed when the scale is started. The calibration counter is now displayed which is incremented whenever the scale is recalibrated. It enables the user to check whether the scale was manipulated. If, within five seconds, the button is pressed longer than 1.5 s, the scale switches to recalibration mode. The scale now measures the zero point and waits to be loaded with at least ¼ of the maximum load. By briefly pressing the button the weight displayed can be decremented or incremented in steps of 10g until the weight of the load placed on the scale is reached. The direction can be changed by pressing the button longer. To stop recalibration the button must be pressed longer than 5s. The scale can be switched off any time using the on/off button or by not activating it for a while, thus aborting recalibration.

Optional functions (only DMS low-end module and SLC highend)

The functions “Tare“, “Hold“, “Autohold“ and “Replace weight in repeat measurements” can be implemented via a program on the EEPROM. The functions are explained below:

Tare:
The tare function can be assigned to a button by the EEPROM program. If the button is pressed, the weight is tared off as soon as the display has settled, if it is within the permissible range. Pressing the button again alternatively switches the tare function off or causes the weight to be tared off again.

Hold and Autohold:
If the hold function is assigned to a button by means of the EEPROM, the weight reading is held on display when the button is pressed as soon as the value has stabilized. Alternatively, the hold function can be automated so that the weight will always be frozen when it has exceeded a certain threshold and is stable.

The hold function is switched off after expiry of a predetermined time or by pressing the button again. In addition the scale can be configured so that the hold function will be deactivated when the scale is relieved, when the scale is relieved and then loaded again and / or when the load on the scale changes significantly.

Replace weight in repeat measurements:
The scale can be configured so that the weight last displayed is displayed again in a measurement when the scale detects that it has been loaded with almost the same weight.

Seca 703 Calibration

To ensure that the module functions properly, data must be written to the EEPROM before the module is calibrated. Values that are only determined during the calibration process can be set to 0. The correct figures will then be set after calibration. If the weight is to be calculated using a third order polynomial, the scale must be calibrated using at least four test loads. In order to increase accuracy, it is recommended to use even more weights. If you wish to configure individual temperature compensation, the scale must be measured with a load and without a load at temperatures on different ends of the range. In order to determine the square term for slope compensation, the scale must also be measured at an average temperature. To determine the required calibration values, please refer to the relevant documentation for EEPROM programming.

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