Product Description

The single–width MXD 5121 (Cat. No. 560) is specifically designed to drive the 512–Channel Flying Capacitor Scanner (FCS) in conjunction with a suitable ADC module such as the 12 bit ADC 1232–2 or the 14 bit ADC 1432.

The general arrangement of the 512 channel Flying Capacitor Scanner, front view, is shown in Fig 1, and the FCS 256 bin rear view, in Fig 2. Briefly, 16 analog signals from Plant elements such as thermocouples, resistance thermometers, strain gauges etc. enter each FCS 16 card at the upper connector, there being up to 16 such cards in an FCS 256 bin, and up to two bins to a scanner. Under the control of the MXD 5121 CAMAC module, through a BA16 (Buffer Amplifier) card in each FCS 256 bin, one FCS 16 card is chosen in each bin, the buffer amplifier gains are software set appropriately, each of 16 or 32 flying capacitors is connected via relays to the Plant Signal, then to the analog bus, buffered onto the front Analog ribbon cable and presented to the ADC module. The MXD 5121 then triggers the ADC to scan all 32 inputs, receiving back a ’done’ signal when all have been converted, and it then sets its LAM flag announcing ’converted data ready’. When the 32 values have been read, the MXD 5121 is instructed to select another pair of FCS 16 cards (setting the buffer gains appropriately) and the sequence is followed on the new data. This is explained in more detail in the FCS data sheet.

Operation

First the gain (X1 or X50) must be set on the 16 buffer amplifiers on the BA16 card in bin 1 (and bin 2) for the first group of 16 (+16) inputs. This is done with A(2),F(17) for bin 1 and A(3),F(17) for bin 2, in each case each of 16 amplifiers is individually set to X1 or X50 by the corresponding W line being at 0 or 1; the same gain pattern will be used for every group of inputs until changed. Then the command A(0),F(17) is used to load the Scan Control Register, indicating both which one of 16 groups (of 16 or 32 inputs) is to be selected and, with the OC bit, whether this is to be a normal input scan or an open–circuit–detection scan; in which the flying capacitors are charged to a reference voltage, connected to plant and then measured; the command also initiating the appropriate scan sequence.

Considering operation on two bins, the scan sequence is as follows. One channel of the basic flying capacitor schematic is shown in Fig 3 (see FCS 512 data sheet for details). All contacts are normally open, and the sequence starts with the MXD 5121 applying ’SELECT IN’, closing all ’IN’ contacts. This is done via two lines on the approriate control ribbon: SELECT STROBE and IN/OUT (IN = 0, OUT = 1). The BA16 unit takes these two, in conjunction with the Group Address bits, to operate the 16 IN or OUT relays on the selected Group (FCS 16) in its bin. They stay closed for a length of time governed by the settings of the delay bit switches D1 and D2 on the FCS 16 card, the MXD 5121 having timing circuits which may be used to select 4 delay times corresponding to D2D1 of 00, 01, 10 or 11, preset from ’short’, 1/8S, 1/4S, 1/2S, 1S, 2S, or 4S, ’short’ being separately presettable from 50 mS to 126 mS. The point of all this is that the IN contacts should be closed for 10 time–constants, and a wide range of time constants may be implemented using different signal conditioning elements, Of course, circuits must be grouped so that all on one (+ one) FCS 16 card can tolerate the same delay time.

At the end of the preset delay selected for the particular group, the MXD releases SELECT IN and, after a further 3 mS delay to ensure all IN relays have dropped out, asserts SELECT OUT to connect the charged capacitors via the OUT contacts to the analog bus, and thus to the ADC via the individual buffer amplifiers in the BA16 card.

Open Circuit Detection

When selected, this reverses the above operation; each capacitor on an FCS 16 card is charged to 3.5V via the OUT relays which are then released. Closing the IN relays then allows this charge to short through the thermocouple or other input source. Normal operation then measures how much is left; if virtually all of it is, the input source must be open circuit.

Dataway Command Set

F1,A12	Read LAM Status Register. ’Q’ = 1.
F1,A13	Read LAM Mask Register. ’Q’ = 1.
F1,A14	Read LAM Request Register. ’Q’ = 1.
F8,A15	Test LAM, if set ’Q’ = 1.
F9,A0	Clear LAM Mask and Status Registers, also Busy Bistable. ’Q’ = 1.
F17,A0	Select next group of 16 plus 16 FCS 512 capaacitors and initiate scan.
	If ’OC’ is set, the addressed group are used in ’Open–Circuit–Detection’ mode; gain must be set to ’1’. ’Q’ = 1.
F17,A2	Select gain of 16 amplifiers (individually) in BA16 of bin 1; corresponding W1 to W16 line equals 0 or 1 for X1 or X50. ’Q’ =1.
F17,A3	Select gain of 16 amplifiers in BA16 of bin 2. ’Q’ = 1.
F19,A12	Selective bit set LAM Status Register W1 to W16. ’Q’ = 1.
F19,A13	Selective bit set LAM Mask Register W1 & W2. ’Q’ = 1.
F23,A12	Selective bit clear LAM Status Register W1 to W16. ’Q’ = 1.
F23,A13	Selective bit clear LAM Mask Register W1 & W2. ’Q’ = 1.
Z.S2	Same as F9,A0.
C,I	Not used.
X	Given for all addressed commands.

The LAM Status Register has the following bit allocation:–

The bits are D, Data Ready; E, Error Present (’OR’ of bits 9 to 11); NS, Not Set; NC, Not cleared (within 18 mS.); MUX E (Error), no FCS 16 selected, or more than one in the same bin selected; and OC and address bits as in Scan Control Register. The D and E bits alone can generate a LAM Signal, in association with corresponding LAM Mask and LAM Request Registers.

Module Power Details

The MXD 5121 requires 1 Amp at +6 Volts.

Test Point Details

There are 10 test points used as follows:-