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4.12 EEPROM Checksum error
Each time calibration or setting data is written to EEPROM (non-volatile memory) by the positioner circuit, a checksum of all EEPROM data is calculated and written to EEPROM. Hence if there is a power supply (i.e. signal) interruption during the EEPROM write procedure, the checksum will not be written correctly, or at all. After the interruption, during its initialization routines the positioner carries out a checksum calculation of the data stored in EEPROM. If the newly calculated checksum and the stored checksum are not identical, the positioner enters an error routine, and does not start Normal Mode operation. This condition is indicated by the LEDs lighting one after the other in sequence. If this condition is achieved, carry out the reset procedure described in section 4.3, and then recalibrate as detailed in sections 4.5 to 4.8.
4.13 Selecting and Setting Up Non-Linear Curves.
The positioner may be operated either as a linear or non-linear device. Non-linear operation is enabled by fitting a jumper link to the positioner with the positioner (and position retransmit if fitted) powered down (i.e. input current at 0 mA). When the positioner is powered up with the link “on” (see figure 6 for its position), it will then operate as a non-linear device for as long as it remains powered up. Conversely, when the positioner is powered up with the link “off”, it will operate as a linear device as long as it remains powered up. Changing the link from “on” to “off” or vice-versa while the circuit remains powered up will not cause a change from non-linear to linear operation – the position of the link is only effective during power up.
When the positioner is powered up with the jumper link “on” and the air supply connected, then any one of eleven characteristic curves may be selected. Press the SET button to go into Setup Mode, and select the CURVE variable by pressing the UP button until the CURVE LED lights continuously. It is easiest to select the required curve from the eleven available by setting the input signal current to midway between the LCP and HCP signal current values – for instance, if the LCP is 4 mA and the HCP is 20 mA, then set the input current to 12 mA for this purpose.
With the signal set at midway between LCP and HCP values, select Adjust Mode by pressing the SET button, and the CURVE LED will now blink. The default curve is in fact the linear curve midway between the other non-linear curves (see Figure 8). To select one of the other curves, press the UP or the DOWN button, and observe the movement of the positioner as its position conforms to the intersection of the mid value signal with the different curves selected from those defined in Figure 8. Each button press steps from one curve to the next one, until at the last curve further button presses have no effect. When the desired curve has been selected, press the SET button to return to Setup Mode.
Note: As soon as the UP or DOWN button has been pressed to select a particular curve, the new curve selection is stored in non-volatile memory and is retained even if the positioner is de-energised before leaving Adjust and Setup Modes.
Each curve is scaled between the two calibration points LCP and HCP. If input currents are reduced below LCP current or increased above HCP current, the positioner stops dead at the LCP or HCP position respectively. This is in fact the difference between the linear curve selected as the default “non-linear” curve, and the linear curve selected when the positioner is powered up with the jumper “off” - the latter gives positions extrapolated on the the same linear characteristic beyond the LCP and HCP signals, whereas the former stops dead at the LCP and HCP positions.
4.14 Setting Optional Angle Retransmit Span and Zero Adjustments.
The angle retransmit circuit is mounted directly underneath the positioner circuit, and its