Westermo RM-505U-K - Manual (Page 11)

man_505U-K_1.4.doc Dec 2008
    ELPRO Technologies Pty Ltd 2008 Page 11
2.4.3 Shaft Encoder Inputs
The two pulse inputs may be configured to control one up/down count value, for use with
quadrature and incremental shaft encoders. A shaft encoder is a transducer that measures
level or displacement, and has two pulse signals to indicate change of level and direction of
change. Both pulse inputs are read at the same time. The divider parameter on PI2 must be
set to 1 for this application.
If an incremental encoder is used, then the calculated count value is stored in PI1. If a
quadrature encoder is used, then the calculated count value is stored in PI2.
The counter value (or “level position”) can be manually set using the 905K diagnostics
features (refer section 5 of this manual). Initially the counter will need to be “zeroed” when
the shaft encoder is in the “zero level” position.
2.4.4 Pulse Rates
The rate of each pulse count is calculated and can be transmitted as internal analogue inputs.
The rate is calculated on the increase of the base counter, not the rate of the input pulses. The
maximum count rate which can be calculated is 1000Hz. For PI1, this is the maximum pulse
rate that can be calculated. For PI2, a divider can be used for pulse rates more than 1KHz.
The pulse rate values can be scaled - that is, the user can configure what pulse rate (0.1 –
1000Hz) corresponds to maximum analogue value (20mA). Each pulse rate can be scaled
individually. Note that this is separate to the divider on PI2 count.
If the pulse inputs are configured for a shaft encoder, a pulse rate is still calculated -
corresponding to rate change of level. A zero rate (“steady level”) will correspond to a 50%
analogue signal. The analogue signal will be more than 50% if the level is increasing, and
less than 50% if the level is decreasing. If an incremental shaft encoder is used, then the rate
may be scaled by scaling PRATE1. If a quadrature encoder is used, scale PRATE2. The
scaling value will determine both the 100% analogue signal (e.g. 20mA) and 0% signal (e.g.
4mA). For example, if a maximum pulse rate of 10Hz is configured, then the analogue
signal will be:
100% if the encoder increases at 10Hz 50% if the encoder pulse rate is 0
0% if the encoder decreases at 10Hz. 75% if the encoder increases at 5Hz
25% if the encoder decreases at 5Hz
Note that this is only true if the pulse inputs are configured for a shaft encoder. If standard
pulse inputs are used, then 0% analogue signal will correspond to zero pulse rate (0Hz).
The pulse rates are treated as analogue inputs and follow the rules for an analogue input as
described below.
2.4.5 Analogue Inputs
The analogue input can measure from 0 – 24mA or 0 – 10VDC. Current or voltage input can
be selected by an internal selector (refer Installation section of this manual). The mA input
can be used for conventional 4-20mA signals or 0-10mA or 0-20mA. The voltage input can
be used for 0-5 or 0-10VDC signals. The 505K unit is factory configured for a 4-20mA
signal, however the user can calibrate the unit for other ranges. The measurement resolution
is 12 bit.
The analogue input uses a “sample time” and “warm-up time” configured by the user. The