Connections

All connections to the VP550 are made via the terminal blocks within the VP550 enclosure.

• To open the enclosure:
  (1) Carefully remove the cover strips at the top and bottom of the fascia.
  (2) Unscrew the four securing screws.
  (3) Gently separate the two halves of the enclosure, which are connected by a ribbon cable (and a cable to the USB socket, if fitted).
  (4) When connections are completed, carefully reassemble the unit and replace the cover strips.
• Connection information is given in the following sections:

1.1 Power supply

• Use a smoothed, low-noise DC power supply providing 24V DC (tolerance ± 10%). If earthed, ensure it is connected to a “clean” (instrument) earth*.
• The power supply must:
  (1) provide 250mA (6W) minimum, and
  (2) derive its output from a source not exceeding 250V DC or 250V rms AC.
• Protect the power circuit by a 250mA slow-blow fuse in the positive line.
• Connect the power supply to terminals 1 (+24V) and 2 (0V) of Terminal Block 1 (TB1) in the VP550 (Figure 3).
• Connect terminal 3 of TB1 to a “clean” (instrument) earth (Figure 3). Note that this also gives the power supply a DC route to earth.

*I.e. an earth to which only low-noise devices such as meters, sensors or chart recorders are connected. High-noise devices such as pumps and motors should be earthed separately.

1.2 Connections

Most viscometer models connect directly to the relevant terminals in the transducer interface section (terminals 4-10 on Terminal Block 1).

• For details of transducer connections, see the User Manual for the transducer.
• All signal cables must be individually screened as indicated.
• The serial communications indicator LED flashes whenever data transfer takes place between the transducer and the VP550.
• The indicator flashes red when the VP550 is transmitting and green when the VP550 is receiving.

1.3 Density input

The VP550 can accept a 4-20mA analogue signal from an external density meter.

• See Figure 4 for Safe Area connection details. For intrinsically safe installations, be sure to use a suitable barrier and follow all relevant guidelines and recommendations.
• For initial setup, see Section 3.3.2. For input selection, see Section 4.1.

1.4 Temperature input

The VP550 can accept input from either

• It is not possible to use both types of input at the same time.

1.4.1 Intrinsically safe systems: PRT input

• For intrinsically safe systems, connect the PRT to the VP550 through a suitable Zener Barrier located in the Safe Area, as shown in Figure 5. The system is NOT intrinsically safe if the barrier is not connected.
• Ensure the relevant IEC Code of Practice is rigorously followed.
• All cable must be certified for intrinsically safe systems (500V rms insulation rated).
• Ground any spare cable cores and screens to barrier ground.

1.4.2 Intrinsically safe systems: 4-20mA temperature input

• For intrinsically safe systems, connect the temperature transmitter to the VP550 through a suitable Zener Barrier located in the Safe Area, as shown in Figure 6. The system is NOT intrinsically safe if the  barrier is not connected.
• Ensure the relevant IEC Code of Practice is rigorously followed.
• All cable must be certified for intrinsically safe systems (500V rms insulation rated).
• Ground any spare cable cores and screens to barrier ground.

1.4.3 Safe Area systems: PRT input

• For Safe Area systems, connect the PRT as shown in Figure 7.

1.4.4 Safe Area systems: 4-20mA temperature input

• For Safe Area systems, connect the temperature transmitter as shown in Figure 8.

1.5 Pressure

The VP550 can accept a 4-20mA analogue pressure input signal.

• See Figure 9 for Safe Area connection details. For intrinsically safe installations, be sure to use a suitable barrier and follow all relevant guidelines and recommendations.

1.6 4-20mA analogue outputs

Three 4-20mA analogue outputs are available, at terminals 1-9 on Terminal Block 3.

• See Figure 10 for Safe Area connection details. For intrinsically safe installations, be sure to use suitable barriers and follow all relevant guidelines and recommendations.
• Burden resistance: 1000 ohms for a 24V power supply. The maximum load may be less if the supply voltage at the VP550 is less than 24V.
• For setup and scaling, see Section 3.3.6.

1.7 RS485 serial data link

• RS485 serial data is available from terminals 5-8 on Terminal Block 4.
• The serial data link can be wired in either a two-wire or a four-wire configuration (Figure 11).
• The serial data link uses a version of the Modbus® protocol (ASCII or RTU)*. For details, see Appendix 2 ASCII) or 3 (RTU).
• For settings, see Section 3.3.5.

*Modbus is a registered trademark of Gould Modicon Inc.

1.7.1 Multidrop configuration The RS485 serial communications may be used to bus-connect a number of units in a multidrop configuration. When connecting the units, ensure that: 1. connecting wires are taken right to the relevant terminal block in each VP550 (so that there are no external junctions), and 2. on header LK3 (located below Terminal Block 4 in the VP550) (Figure 12), the jumper link must be positioned across pins 1 and 2 in every unit except the last in the chain. In the last unit, the link must be positioned between pins 2 and 3 (Figure 13).

1.8 USB output (optional)

The VP550 may be supplied fitted with a mini USB-B socket located on the left-hand side of the enclosure. Suitable USB connection cables are available from the Bulgin Buccaneer range. The relevant USB driver must be installed on the computer to which the VP550 is to be connected (see Appendix 4).

1.9 Relays

The VP550 has two volt-free relay contacts which can be used for alarm purposes.

• Contacts are rated at 1A @ 30V.
• The alarm condition can be individually set as either contacts open or contacts closed by positioning the relevant jumper links LK1 and LK2 on the circuit board. For connection details, see Figure 14.
• For setup details, see Section 3.3.4.
• The VP550 will show an alarm condition if the minimum and/or maximum limits are surpassed.