Gradient Controller

This section covers the use of the LCD CONTROLLER for stand-alone gradient pumps. For front-panel control of isocratic pumps, see the MANUAL CONTROLS section. For computer control see the PUMP section under Operation With ChromGraph Control.



Before operating in the gradient mode you must connect the mobile phases and switch from the pulse damper to the mixer. See the INSTALLATION section for details.





The LCD controller connects to the SYSTEM DIRECTOR port on the back panel. It takes over all functions from the front panel when the LOCAL/REMOTE switch is in the REMOTE position. The controller can edit and store up to seven methods. Programming the controller is best learned by the hands-on approach. The following guidelines will make this process smoother.

The row of blank buttons directly under the display become active when function labels appear in the display just above them.

Use the ENTER key to scroll horizontally across lines of information.

Use CLEAR to remove an erroneous entry.

The cursor cannot back up. If you enter an erroneous entry, complete the line and come back to it with the UP arrow key.

Use DELETE to remove an entire line of information. The cursor must be on the left side of the line for DELETE to be active.

Use UP and DOWN arrows to scroll vertically among lines. The cursor must be on the left side of the line for these keys to be active.

To SAVE a modified method, you must press two save functions. The first saves the method to RAM, the second saves it to permanent storage under a file number from 1-7.

STATUS will toggle to a status screen that shows pump conditions and run time:

Press STATUS again to return to the previous screen. STATUS is active at all times.




Gradient operation generally requires a timed program in which the proportion of mobile phase from the bottles varies with time. However, many routine operations, such as cleaning columns and setting up initial conditions, require only that the pump be started at a specified flow rate and mobile-phase mix. These manual operations can be set into effect with a few keystrokes. For example, to set up the initial conditions of 80% A, 20% B, 1 mL per minute, do the following:


  1. Turn on the main power and set the pump for REMOTE operation. The LCD will come on, do some self checks and ask you to press any key. The screen will then look like this:


  2. Press the key below the word PUMP, and the screen below will appear. This is the main programming screen for the pump.


  3. The cursor will appear at the top right of the screen, with a default of 1. The two valid choices here are:


    • 1 = normal flow rates, 0-5 mL per minute in 0.1 mL increments.
    • 2 = microbore flow rates, 0-0.5 mL per minute in 0.01 mL increments.

    Choose normal flow rates by pressing ENTER. (To choose microbore, key in a "2", then press ENTER.)


  4. The cursor then moves down to the high- and low-pressure cutoffs, which should be set for most uses at 4000 and 200 PSI. Press ENTER to accept these defaults.


  5. The cursor is now at the 0.0 time line. Press ENTER to move to the FLOW column, and change it, if necessary. Then press ENTER to move to the % A column. Press ENTER if it is correct (80.0% in this example), or key in the correct percentage, then press ENTER. The % B column is done similarly. The % C column is calculated automatically as the difference between A+B and 100%.


  6. The cursor should now be at the start of line 2 (even if it is a blank line). Press EXEC to start the pump with the conditions set in the 0.0 time line. The STOP button will stop the pump, and the SAVE button is the first of the two-step process to make the file permanent. Pressing SAVE will bring up the Save File Screen:

    File numbers 1-7 are valid entries for up to 7 stored methods. Change the file number if necessary, then press SAVE again to complete the process.


  7. If you do not want the current pump conditions to become part of a permanent method (e.g., you are flushing the column with an organic solvent), do not SAVE the instructions. When you wish to recall the original program, use the ESCAPE button. The following LCD screen will appear:

    Press PUMP and the following screen will appear:

    The temporary instructions are lost and the original instructions have reappeared. The pump will still be carrying out the temporary instructions, but pressing EXEC will reinstate the original instructions.





Purge instructs the pump to automatically modify flow rate to maintain a given pressure. If the preset pressure is not reached, the pump will gently increase flow rate to its maximum of 5 mL per minute. A purge is useful to wash a column, or to bring fresh mobile phase from the solvent reservoirs up to the prime/purge valve. To begin a purge:


  1. Start from the main programming screen:


  2. Press the key under the PURGE label. The purge control screen will appear:


  3. Enter the percentages to be metered from each solvent reservoir, and the pressure that the pump should attempt to hold. A valid pressure range is between 0 and 5000 PSI.


  4. Enter the duration of the purge (0.1 - 99.9 minutes).


  5. The purging information can be saved, if desired, by pressing SAVE in this screen, SAVE in the main programming screen, and SAVE in the Save File screen.


  6. ESCAPE will return to the main programming screen.


  7. Before beginning the purge:


    • If the purge is to bring fresh mobile phase up to the prime/purge valve, put a 50-mL disposable syringe on the valve, and open the valve one turn.


    • If the purge is to wash a column, make sure the maximum pressure setting does not exceed the working pressure of the column, and that the prime/purge valve is closed.


  8. Press PURGE to start the purge cycle. The pump will slowly increase flow rate until it hovers around the preset pressure. If the preset pressure is not reached, the pump will increase its flow rate to 5 mL per minute.


  9. At any time during the purge, ESCAPE will end the purge, and STATUS will bring up the status screen.





A program (a series of timed events) must be used whenever a gradient is needed, and whenever the pump must be synchronized with peripheral equipment (such as an autosampler).

Before beginning a gradient, check that pump synchronization is turned on. Synchronization ensures precise, repeatable gradients by delaying the start of each run until a specific piston position is reached.

Program a gradient as follows:


  1. Start at the main programming screen:


  2. Assuming the FLOW RANGE, MAX and MIN settings are correct, press ENTER three times to put the cursor at the left of the 0.0 time line.


  3. Enter the FLOW and bottle percentages as appropriate for the 0.0 time line (initial conditions).


  4. The cursor will automatically begin the second time line. Enter the time (minutes) and bottle percentages for this line (there is no FLOW programming, so the FLOW column will be blank).


  5. A program must have at least two time lines: a start (0.0) line and an end line. Up to ten lines are permitted. Note that:


    • A linear gradient will be performed between any two time lines that differ in bottle percentages.
    • Any time period in which the solvent mix does not change must be indicated by bracketing it with time lines that do not differ in bottle percentages.


  6. Only three time lines will fit on the screen simultaneously. The lines will scroll up during entry of subsequent lines. For review of hidden lines, move the cursor to the left side of a line and use the UP and DOWN arrows.


  7. Use DELETE to remove an entire line, use CLEAR to change an erroneous entry.


  8. Lines can be entered in any order and will sort themselves out on the screen.


  9. After the last entry, press SAVE in the programming screen and SAVE in the Save File screen.


  10. To start the pump under the conditions in the 0.0 time line, press EXEC in the main programming screen or EQUIL in the equilibration screen:

Begin gradient operation as follows:


  1. From the equilibration screen press EQUIL. The pump will start, and the Equilibrating Screen will appear:

    This indicates that the program is ready to begin. Note that there is a difference between the Equilibration screen (i.e., ready to equilibrate) and the Equilibrating screen (i.e., already equilibrating, ready to run).


  2. Press INJECT to start the run. Depending on the options you have selected under CONFIGURATION, the run may start immediately, or after a delay for synchronization. If AUTO RUNS was selected, you will be asked to enter the number of runs desired. When the run starts, the Run in Progress screen appears:


  3. STATUS may be pressed at any time during a run. However, the RUN IN PROGRESS screen must be visible for the run to end properly and for subsequent runs to begin (i.e., do not leave the controller in status mode).


  4. ABORT terminates the gradient run and returns to the 0.0 time conditions.


  5. STOP terminates the gradient run and stops the pump.


  6. PAUSE will halt the clock and maintain the current mobile phase composition indefinitely. The PAUSE button will change to CONTinue, which should be pressed to resume the run.


  7. You can make changes to the pump program and save it at any time. However, the old program will still be in effect. To put the new program into effect, press ABORT then EQUIL.


  8. The run will end when the last time line of the program is reached. The Equilibrating screen will appear, and the zero-time conditions will be maintained. If AUTO RUNS was selected, the next run will start. If not, the pump will await a signal from the operator or autosampler.





Certain options are available to control the behavior of the pump in gradient and non-gradient operations, and for communication with an autosampler. To reach the hardware configuration screen, do the following:


  • From initial startup, follow the PUSH ANY KEY TO CONTINUE instruction. A screen with software versions will appear. Press any key to continue. The next screen says PRESENT EDIT FILE=1" at the top left:


  • Press the CONFIG key. The Configuration Screen appears:


  • To get to the configuration screen from the main programming screen, press SAVE, then SAVE in the next screen, then METHOD in the equilibration screen, then the CONFIG button.


  • Options 1 and 2 (detector options) are invalid in this application. Set them to "0".


  • Option 3: PUMP SYNCHRONIZATION. Turn synchronization on with a "1", off with a "0". Pump synchronization ensures that each gradient run starts with the pistons in the same relative positions, for precise control of retention times. ALWAYS TURN SYNCHRONIZATION ON FOR GRADIENT OPERATION. Synchronization may be left on or off for isocratic operation. The synchronization process causes a slight delay (up to 12 seconds at 1 mL/min) before each run starts. At microbore flow rates this delay will be noticeable (up to 120 seconds at 100 µL/min).


  • Option 4: AUTO RUNS. With certain kinds of autosamplers, we want the PM-80 pump to be in control and signal the autosampler to inject. (See AUTOSAMPLERS below.) In this situation, turn AUTO RUNS on ("1") so the pump will initiate subsequent runs automatically. When AUTO RUNS is on, you will be asked "HOW MANY RUNS" when you press INJECT to start the runs. You will also be asked for the "NEXT FILE NUMBER", which allows the chaining of several methods.


  • Option 5 provides onscreen diagnostics for use by our engineers. May be left on or off.


  • Option 6 is invalid in this application. Set it to "0". Press ENTER to continue.


  • Press SAVE to exit and institute whatever changes were made.





The PM-80 gradient pump can communicate with autosamplers for automatic operation. The specific procedure to be used depends upon the type of autosampler that is available. (This discussion assumes a stand-alone pump. If this is an epsilon computer-controlled system, see the AUTOSAMPLER section.)

BAS Sample Sentinel Autosampler

The Sample Sentinel autosampler is capable of two-way communication with the PM-80 pump. Two-way communication ensures that no injections will occur if either unit malfunctions. Connect the units as follows (click here for a view of the pump's rear panel).


Autosampler Pin Pump Terminal
1 Gnd
7 Inject
8 Ready

When programming the autosampler, make sure that the it's run length is a minute or two longer than that of the pump. This ensures that the pump is in the EQUILIBRATING screen when the autosampler sends its READY signal. You also must change 'Inject Hold Active' to HI on the autosampler's input polarity menu.

In the pump's configuration screen, AUTO RUNS should be off. To start the sequence of runs, program the pump. Then press SAVE, SAVE, and EQUIL. You're now in the EQUILIBRATING screen. Start the autosampler. When it has loaded the sample it will send a READY signal, which triggers the PM-80 to begin the run. The PM-80 sends the INJECT signal to the autosampler when the run begins.

Other Autosamplers: PM-80 In Charge

If an autosampler is not capable of two-way communication, but will accept an INJECT signal, the system can be automated with the PM-80 pump in charge. Program the autosampler so it will end its run and load the next sample before the PM-80 has completed its run. The autosampler must then wait for a trigger from the PM-80. Connect leads from the INJECT and GND terminals on the PM-80 to the SAMPLE ENABLE terminals on the autosampler. Turn AUTO RUNS on, which will allow the PM-80 to do a sequence of runs without waiting for a trigger.

To start the sequence, first start the autosampler. When it has loaded the sample and is waiting, bring the PM-80 to the EQUILIBRATING screen. To get here from the main programming screen press SAVE, SAVE, EQUIL). Now press INJECT. Enter the number of runs in the sequence, and the next file number (typically the same as the current file). Press ENTER to accept the file number, and the sequence of runs will begin.

Other Autosamplers: Autosampler In Charge

If the autosampler will not accept an INJECT signal, then the autosampler must be in charge of the run. Pump synchronization must be off, since there is no way to communicate the variable start times to the autosampler. For isocratic runs, simply turn on the pump in the local mode, and let it run while the autosampler injects. For gradients, attach leads to the autosampler terminals that signal when an injection has occurred. Connect these to the READY terminals on the PM-80. Put the PM-80 in the EQUILIBRATING screen, then start the autosampler.